Here's what you do: Have two sprites: one with a platform behavior called Platform sprite and one with all of your animations called Mask sprite.
System every tick,
Then in the action add:
Mask sprite set position to Platform sprite.
If you want to have a separate sprite for your camera, you just add another sprite with the scroll to behavior and follow the same code above. The platform sprite will ensure that your sprite collision box stays the same and will prevent your sprite from "falling" hope this helps!