diff --git a/core/src/main/scala/cats/data/ReaderWriterStateT.scala b/core/src/main/scala/cats/data/ReaderWriterStateT.scala
index 3813094ac0..85c921f43a 100644
--- a/core/src/main/scala/cats/data/ReaderWriterStateT.scala
+++ b/core/src/main/scala/cats/data/ReaderWriterStateT.scala
@@ -41,18 +41,6 @@ final class ReaderWriterStateT[F[_], E, S, L, A](val runF: F[(E, S) => F[(L, S,
   def mapWritten[LL](f: L => LL)(implicit F: Functor[F]): ReaderWriterStateT[F, E, S, LL, A] =
     transform { (l, s, a) => (f(l), s, a) }
 
-  /**
-   * Combine this computation with `rwsb` using `fn`. The state will be be threaded
-   * through the computations and the log values will be combined.
-   */
-  def map2[B, Z](rwsb: ReaderWriterStateT[F, E, S, L, B])(fn: (A, B) => Z)(
-    implicit F: FlatMap[F], L: Semigroup[L]): ReaderWriterStateT[F, E, S, L, Z] =
-    flatMap { a =>
-      rwsb.map { b =>
-        fn(a, b)
-      }
-    }
-
   /**
    * Modify the result of the computation by feeding it into `f`, threading the state
    * through the resulting computation and combining the log values.
@@ -343,6 +331,21 @@ private[data] sealed trait RWSTInstances extends RWSTInstances1 {
     new RWSTMonadTrans[E, S, L] {
       implicit def L: Monoid[L] = L0
     }
+
+  implicit def catsDataProfunctorForRWST[F[_], S, L](implicit F0: Functor[F]): Profunctor[ReaderWriterStateT[F, ?, S, L, ?]] =
+    new RWSTProfunctor[F, S, L] {
+      implicit def F: Functor[F] = F0
+    }
+
+  implicit def catsDataBifunctorForRWST[F[_], E, S](implicit F0: Functor[F]): Bifunctor[ReaderWriterStateT[F, E, S, ?, ?]] =
+    new RWSTBifunctor[F, E, S] {
+      implicit def F: Functor[F] = F0
+    }
+
+  implicit def catsDataContravariantForRWST[F[_], S, L, A](implicit F0: Functor[F]): Contravariant[ReaderWriterStateT[F, ?, S, L, A]] =
+    new RWSTContravariant[F, S, L, A] {
+      implicit def F: Functor[F] = F0
+    }
 }
 
 private[data] sealed trait RWSTInstances1 extends RWSTInstances2 {
@@ -396,38 +399,17 @@ private[data] sealed trait RWSTInstances5 extends RWSTInstances6 {
     }
 }
 
-private[data] sealed trait RWSTInstances6 extends RWSTInstances7 {
+private[data] sealed trait RWSTInstances6 {
   implicit def catsDataFunctorForRWST[F[_], E, S, L](implicit F0: Functor[F]): Functor[ReaderWriterStateT[F, E, S, L, ?]] =
     new RWSTFunctor[F, E, S, L] {
       implicit def F: Functor[F] = F0
     }
 }
 
-private[data] sealed trait RWSTInstances7 extends RWSTInstances8 {
-  implicit def catsDataContravariantForRWST[F[_], S, L, A](implicit F0: Functor[F]): Contravariant[ReaderWriterStateT[F, ?, S, L, A]] =
-    new RWSTContravariant[F, S, L, A] {
-      implicit def F: Functor[F] = F0
-    }
-}
-
-private[data] sealed trait RWSTInstances8 extends RWSTInstances9 {
-  implicit def catsDataBifunctorForRWST[F[_], E, S](implicit F0: Functor[F]): Bifunctor[ReaderWriterStateT[F, E, S, ?, ?]] =
-    new RWSTBifunctor[F, E, S] {
-      implicit def F: Functor[F] = F0
-    }
-}
-
-private[data] sealed trait RWSTInstances9 {
-  implicit def catsDataProfunctorForRWST[F[_], S, L](implicit F0: Functor[F]): Profunctor[ReaderWriterStateT[F, ?, S, L, ?]] =
-    new RWSTProfunctor[F, S, L] {
-      implicit def F: Functor[F] = F0
-    }
-}
-
 private[data] sealed trait RWSTFunctor[F[_], E, S, L] extends Functor[ReaderWriterStateT[F, E, S, L, ?]] {
   implicit def F: Functor[F]
 
-  def map[A, B](fa: ReaderWriterStateT[F, E, S, L, A])(f: A => B): ReaderWriterStateT[F, E, S, L, B] =
+  override def map[A, B](fa: ReaderWriterStateT[F, E, S, L, A])(f: A => B): ReaderWriterStateT[F, E, S, L, B] =
     fa.map(f)
 }
 
@@ -452,7 +434,7 @@ private[data] sealed trait RWSTProfunctor[F[_], S, L] extends Profunctor[ReaderW
     fab.contramap(f).map(g)
 }
 
-private[data] sealed trait RWSTMonad[F[_], E, S, L] extends Monad[ReaderWriterStateT[F, E, S, L, ?]] {
+private[data] sealed trait RWSTMonad[F[_], E, S, L] extends Monad[ReaderWriterStateT[F, E, S, L, ?]] with RWSTFunctor[F, E, S, L] {
   implicit def F: Monad[F]
   implicit def L: Monoid[L]
 
@@ -470,13 +452,6 @@ private[data] sealed trait RWSTMonad[F[_], E, S, L] extends Monad[ReaderWriterSt
         }
       }
     }
-
-  override def map[A, B](fa: ReaderWriterStateT[F, E, S, L, A])(f: A => B): ReaderWriterStateT[F, E, S, L, B] =
-    fa.map(f)
-
-  override def map2[A, B, Z](fa: ReaderWriterStateT[F, E, S, L, A],
-    fb: ReaderWriterStateT[F, E, S, L, B])(f: (A, B) => Z): ReaderWriterStateT[F, E, S, L, Z] =
-    fa.map2(fb)(f)
 }
 
 private[data] sealed trait RWSTMonadState[F[_], E, S, L]
diff --git a/laws/src/main/scala/cats/laws/discipline/Arbitrary.scala b/laws/src/main/scala/cats/laws/discipline/Arbitrary.scala
index 010999387e..d67b4c0b02 100644
--- a/laws/src/main/scala/cats/laws/discipline/Arbitrary.scala
+++ b/laws/src/main/scala/cats/laws/discipline/Arbitrary.scala
@@ -160,6 +160,9 @@ object arbitrary extends ArbitraryInstances0 {
 
   implicit def catsLawArbitraryForReader[A: Arbitrary: Cogen, B: Arbitrary]: Arbitrary[Reader[A, B]] =
     catsLawsArbitraryForKleisli[Id, A, B]
+
+  implicit def catsLawsAribtraryForReaderWriterStateT[F[_]: Applicative, E, S, L, A](implicit F: Arbitrary[(E, S) => F[(L, S, A)]]): Arbitrary[ReaderWriterStateT[F, E, S, L, A]] =
+    Arbitrary(F.arbitrary.map(ReaderWriterStateT(_)))
 }
 
 private[discipline] sealed trait ArbitraryInstances0 {
diff --git a/tests/src/test/scala/cats/tests/KleisliTests.scala b/tests/src/test/scala/cats/tests/KleisliTests.scala
index 546764c033..50ea3673c3 100644
--- a/tests/src/test/scala/cats/tests/KleisliTests.scala
+++ b/tests/src/test/scala/cats/tests/KleisliTests.scala
@@ -121,7 +121,10 @@ class KleisliTests extends CatsSuite {
 
   checkAll("Kleisli[Option, ?, Int]", ContravariantTests[Kleisli[Option, ?, Int]].contravariant[Int, Int, Int])
   checkAll("Contravariant[Kleisli[Option, ?, Int]]", SerializableTests.serializable(Contravariant[Kleisli[Option, ?, Int]]))
-  checkAll("MonadTrans[Kleisli[?[_], Int, ?]]", MonadTransTests[Kleisli[?[_], Int, ?]].monadTrans[Option, Int, Int])
+
+  checkAll("Kleisli[Option, Int, ?]]", MonadTransTests[Kleisli[?[_], Int, ?]].monadTrans[Option, Int, Int])
+  checkAll("MonadTrans[Kleisli[?[_], Int, ?]]", SerializableTests.serializable(MonadTrans[Kleisli[?[_], Int, ?]]))
+
 
   test("local composes functions") {
     forAll { (f: Int => Option[String], g: Int => Int, i: Int) =>
diff --git a/tests/src/test/scala/cats/tests/ListWrapper.scala b/tests/src/test/scala/cats/tests/ListWrapper.scala
index 7bf02bfccb..91187fd6f8 100644
--- a/tests/src/test/scala/cats/tests/ListWrapper.scala
+++ b/tests/src/test/scala/cats/tests/ListWrapper.scala
@@ -97,6 +97,8 @@ object ListWrapper {
 
   val monad: Monad[ListWrapper] = monadCombine
 
+  val flatMap: FlatMap[ListWrapper] = monadCombine
+
   val applicative: Applicative[ListWrapper] = monadCombine
 
   /** apply is taken due to ListWrapper being a case class */
diff --git a/tests/src/test/scala/cats/tests/ReaderWriterStateTTests.scala b/tests/src/test/scala/cats/tests/ReaderWriterStateTTests.scala
index 7cb7fe1ce3..fcd3d9c9b9 100644
--- a/tests/src/test/scala/cats/tests/ReaderWriterStateTTests.scala
+++ b/tests/src/test/scala/cats/tests/ReaderWriterStateTTests.scala
@@ -2,10 +2,11 @@ package cats
 package tests
 
 import cats.data.{ ReaderWriterStateT, ReaderWriterState, EitherT }
+import cats.functor.{ Bifunctor, Contravariant, Profunctor }
 import cats.laws.discipline._
 import cats.laws.discipline.eq._
 import cats.laws.discipline.arbitrary._
-import org.scalacheck.{ Arbitrary }
+import org.scalacheck.Arbitrary
 
 class ReaderWriterStateTTests extends CatsSuite {
   import ReaderWriterStateTTests._
@@ -279,18 +280,30 @@ class ReaderWriterStateTTests extends CatsSuite {
   }
 
   implicit val iso = CartesianTests.Isomorphisms
-    .invariant[ReaderWriterStateT[ListWrapper, String, Int, String, ?]](ReaderWriterStateT.catsDataFunctorForRWST(ListWrapper.monad))
+    .invariant[ReaderWriterStateT[ListWrapper, String, Int, String, ?]](ReaderWriterStateT.catsDataFunctorForRWST(ListWrapper.functor))
 
   {
     implicit val F: Monad[ListWrapper] = ListWrapper.monad
+
     checkAll("ReaderWriterStateT[ListWrapper, String, Int, String, Int]",
       FunctorTests[ReaderWriterStateT[ListWrapper, String, Int, String, ?]].functor[Int, Int, Int])
+    checkAll("Functor[ReaderWriterStateT[ListWrapper, String, Int, String, ?]]",
+      SerializableTests.serializable(Functor[ReaderWriterStateT[ListWrapper, String, Int, String, ?]]))
+
     checkAll("ReaderWriterStateT[ListWrapper, String, Int, String, Int]",
       ContravariantTests[ReaderWriterStateT[ListWrapper, ?, Int, String, Int]].contravariant[String, String, String])
+    checkAll("Contravariant[ReaderWriterStateT[ListWrapper, ?, Int, String, Int]]",
+      SerializableTests.serializable(Contravariant[ReaderWriterStateT[ListWrapper, ?, Int, String, Int]]))
+
     checkAll("ReaderWriterStateT[ListWrapper, Int, Int, String, Int]",
       ProfunctorTests[ReaderWriterStateT[ListWrapper, ?, Int, String, ?]].profunctor[Int, Int, Int, Int, Int, Int])
+    checkAll("Profunctor[ReaderWriterStateT[ListWrapper, ?, Int, String, ?]]",
+      SerializableTests.serializable(Profunctor[ReaderWriterStateT[ListWrapper, ?, Int, String, ?]]))
+
     checkAll("ReaderWriterStateT[ListWrapper, Int, Int, Int, Int]",
       BifunctorTests[ReaderWriterStateT[ListWrapper, String, Int, ?, ?]].bifunctor[Int, Int, Int, Int, Int, Int])
+    checkAll("Bifunctor[ReaderWriterStateT[ListWrapper, String, Int, ?, ?]]",
+      SerializableTests.serializable(Bifunctor[ReaderWriterStateT[ListWrapper, String, Int, ?, ?]]))
   }
 
   {
@@ -298,6 +311,8 @@ class ReaderWriterStateTTests extends CatsSuite {
 
     checkAll("ReaderWriterStateT[ListWrapper, String, Int, String, Int]",
       MonadTests[ReaderWriterStateT[ListWrapper, String, Int, String, ?]].monad[Int, Int, Int])
+    checkAll("Monad[ReaderWriterStateT[ListWrapper, String, Int, String, ?]]",
+      SerializableTests.serializable(Monad[ReaderWriterStateT[ListWrapper, String, Int, String, ?]]))
   }
 
   {
@@ -305,6 +320,8 @@ class ReaderWriterStateTTests extends CatsSuite {
 
     checkAll("ReaderWriterStateT[ListWrapper, String, Int, String, Int]",
       MonadStateTests[ReaderWriterStateT[ListWrapper, String, Int, String, ?], Int].monadState[Int, Int, Int])
+    checkAll("MonadState[ReaderWriterStateT[ListWrapper, String, Int, String, ?]. Int]",
+      SerializableTests.serializable(MonadState[ReaderWriterStateT[ListWrapper, String, Int, String, ?], Int]))
   }
 
   {
@@ -312,6 +329,8 @@ class ReaderWriterStateTTests extends CatsSuite {
 
     checkAll("ReaderWriterStateT[ListWrapper, String, Int, String, Int]",
       MonadCombineTests[ReaderWriterStateT[ListWrapper, String, Int, String, ?]].monadCombine[Int, Int, Int])
+    checkAll("MonadCombine[ReaderWriterStateT[ListWrapper, String, Int, String, ?]]",
+      SerializableTests.serializable(MonadCombine[ReaderWriterStateT[ListWrapper, String, Int, String, ?]]))
   }
 
   {
@@ -319,6 +338,10 @@ class ReaderWriterStateTTests extends CatsSuite {
 
     checkAll("ReaderWriterStateT[ListWrapper, String, Int, String, Int]",
       MonadReaderTests[ReaderWriterStateT[ListWrapper, String, Int, String, ?], String].monadReader[String, String, String])
+
+    // check serializable using Option
+    checkAll("MonadReader[ReaderWriterStateT[Option, String, Int, String, ?], String]",
+      SerializableTests.serializable(MonadReader[ReaderWriterStateT[Option, String, Int, String, ?], String]))
   }
 
   {
@@ -326,6 +349,8 @@ class ReaderWriterStateTTests extends CatsSuite {
 
     checkAll("ReaderWriterStateT[ListWrapper, String, Int, String, Int]",
       MonadWriterTests[ReaderWriterStateT[ListWrapper, String, Int, String, ?], String].monadWriter[String, String, String])
+    checkAll("MonadWriter[ReaderWriterStateT[ListWrapper, String, Int, String, ?], String]",
+      SerializableTests.serializable(MonadWriter[ReaderWriterStateT[ListWrapper, String, Int, String, ?], String]))
   }
 
   {
@@ -335,24 +360,29 @@ class ReaderWriterStateTTests extends CatsSuite {
 
     checkAll("ReaderWriterStateT[Option, String, Int, String, Int]",
       MonadErrorTests[ReaderWriterStateT[Option, String, Int, String, ?], Unit].monadError[Int, Int, Int])
+    checkAll("MonadError[ReaderWriterStateT[Option, String, Int, String, ?], Unit]",
+      SerializableTests.serializable(MonadError[ReaderWriterStateT[Option, String, Int, String, ?], Unit]))
   }
 
   {
-    implicit val F = ListWrapper.monad
-    implicit val S = ListWrapper.semigroupK
+    implicit val F: Monad[ListWrapper] = ListWrapper.monad
+    implicit val S: SemigroupK[ListWrapper] = ListWrapper.semigroupK
 
     checkAll("ReaderWriterStateT[ListWrapper, String, Int, String, Int]",
       SemigroupKTests[ReaderWriterStateT[ListWrapper, String, Int, String, ?]].semigroupK[Int])
+    checkAll("SemigroupK[ReaderWriterStateT[ListWrapper, String, Int, String, ?]]",
+      SerializableTests.serializable(SemigroupK[ReaderWriterStateT[ListWrapper, String, Int, String, ?]]))
   }
 
   {
-    implicit val F = ListWrapper.monad
+    implicit val F: Monad[ListWrapper] = ListWrapper.monad
 
-    checkAll("MonadTrans[ReaderWriterStateT[?[_], String, Int, String, ?]]",
+    checkAll("ReaderWriterStateT[?[_], String, Int, String, ?]",
       MonadTransTests[ReaderWriterStateT[?[_], String, Int, String, ?]].monadTrans[ListWrapper, Int, Int])
     checkAll("MonadTrans[ReaderWriterStateT[?[_], String, Int, String, ?]]",
       SerializableTests.serializable(MonadTrans[ReaderWriterStateT[?[_], String, Int, String, ?]]))
   }
+
 }
 
 object ReaderWriterStateTTests {
@@ -364,10 +394,6 @@ object ReaderWriterStateTTests {
     }
   }
 
-  implicit def RWSTArbitrary[F[_]: Applicative, E, S, L, A](
-    implicit F: Arbitrary[(E, S) => F[(L, S, A)]]): Arbitrary[ReaderWriterStateT[F, E, S, L, A]] =
-    Arbitrary(F.arbitrary.map(ReaderWriterStateT(_)))
-
   implicit def RWSTEq[F[_], E, S, L, A](implicit S: Arbitrary[S], E: Arbitrary[E], FLSA: Eq[F[(L, S, A)]],
     F: Monad[F]): Eq[ReaderWriterStateT[F, E, S, L, A]] =
     Eq.by[ReaderWriterStateT[F, E, S, L, A], (E, S) => F[(L, S, A)]] { state =>
diff --git a/tests/src/test/scala/cats/tests/StateTTests.scala b/tests/src/test/scala/cats/tests/StateTTests.scala
index 63c45cb1d6..e697f93460 100644
--- a/tests/src/test/scala/cats/tests/StateTTests.scala
+++ b/tests/src/test/scala/cats/tests/StateTTests.scala
@@ -199,7 +199,7 @@ class StateTTests extends CatsSuite {
 
   {
     // F has a Functor
-    implicit val F: Functor[ListWrapper] = ListWrapper.monad
+    implicit val F: Functor[ListWrapper] = ListWrapper.functor
     // We only need a Functor on F to find a Functor on StateT
     Functor[StateT[ListWrapper, Int, ?]]
   }
@@ -235,7 +235,7 @@ class StateTTests extends CatsSuite {
 
     checkAll("StateT[ListWrapper, Int, Int]", MonadTests[StateT[ListWrapper, Int, ?]].monad[Int, Int, Int])
     checkAll("Monad[StateT[ListWrapper, Int, ?]]", SerializableTests.serializable(Monad[StateT[ListWrapper, Int, ?]]))
-    checkAll("MonadTrans[StateT[?[_], Int, ?]]", MonadTransTests[StateT[?[_], String, ?]].monadTrans[ListWrapper, Int, Int])
+    checkAll("StateT[ListWrapper, Int, Int]", MonadTransTests[StateT[?[_], String, ?]].monadTrans[ListWrapper, Int, Int])
     checkAll("MonadTrans[StateT[?[_], Int, ?]]", SerializableTests.serializable(MonadTrans[StateT[?[_], Int, ?]]))
 
     Monad[StateT[ListWrapper, Int, ?]]
diff --git a/tests/src/test/scala/cats/tests/WriterTTests.scala b/tests/src/test/scala/cats/tests/WriterTTests.scala
index bf16d48fbf..1c9362be3e 100644
--- a/tests/src/test/scala/cats/tests/WriterTTests.scala
+++ b/tests/src/test/scala/cats/tests/WriterTTests.scala
@@ -144,7 +144,7 @@ class WriterTTests extends CatsSuite {
   // resolution and the laws of these various instances.
   {
     // F has an Apply and L has a Semigroup
-    implicit val F: Apply[ListWrapper] = ListWrapper.monadCombine
+    implicit val F: Apply[ListWrapper] = ListWrapper.applyInstance
     implicit val L: Semigroup[ListWrapper[Int]] = ListWrapper.semigroup[Int]
 
     Functor[WriterT[ListWrapper, ListWrapper[Int], ?]]
@@ -166,7 +166,7 @@ class WriterTTests extends CatsSuite {
 
   {
     // F has a Monad and L has a Semigroup
-    implicit val F: Monad[ListWrapper] = ListWrapper.monadCombine
+    implicit val F: Monad[ListWrapper] = ListWrapper.monad
     implicit val L: Semigroup[ListWrapper[Int]] = ListWrapper.semigroup[Int]
 
     Functor[WriterT[ListWrapper, ListWrapper[Int], ?]]
@@ -192,7 +192,7 @@ class WriterTTests extends CatsSuite {
   }
   {
     // F has a FlatMap and L has a Monoid
-    implicit val F: FlatMap[ListWrapper] = ListWrapper.monadCombine
+    implicit val F: FlatMap[ListWrapper] = ListWrapper.flatMap
     implicit val L: Monoid[ListWrapper[Int]] = ListWrapper.monoid[Int]
 
     Functor[WriterT[ListWrapper, ListWrapper[Int], ?]]
@@ -219,7 +219,7 @@ class WriterTTests extends CatsSuite {
 
   {
     // F has an Applicative and L has a Monoid
-    implicit val F: Applicative[ListWrapper] = ListWrapper.monadCombine
+    implicit val F: Applicative[ListWrapper] = ListWrapper.applicative
     implicit val L: Monoid[ListWrapper[Int]] = ListWrapper.monoid[Int]
 
     Functor[WriterT[ListWrapper, ListWrapper[Int], ?]]
@@ -246,7 +246,7 @@ class WriterTTests extends CatsSuite {
 
   {
     // F has a Monad and L has a Monoid
-    implicit val F: Monad[ListWrapper] = ListWrapper.monadCombine
+    implicit val F: Monad[ListWrapper] = ListWrapper.monad
     implicit val L: Monoid[ListWrapper[Int]] = ListWrapper.monoid[Int]
 
     Functor[WriterT[ListWrapper, ListWrapper[Int], ?]]