Rotom changes has these forms: Normal, Heat, Mow, Freeze, Fan, Wash.
They have these moves respectively: None, Overheat, Leaf Storm, Blizzard, Air Slash, Hydro Pump
Pikachu Have these forms: Normal, Rock Star, Belle, Pop Star, Ph. D, Libre, Ash Hat
They have these moves respectively: Surf (only form that can have, Pikachu doesn't learn upon changing form, however), Meteor Mash, Icicle Crash, Draining Kiss, Electric Terrain, Flying Press, (10,000 Volt Thunderbolt Z Move, Pikachu doesn't learn upon changing form, because this one cannot change form)
(Ash Hat and Normal Pikachu can have Volt Tackle via move tutor at Hano Grand Resort)
Source, Source, Source