How to make the entity / player float on fluid?

Simple answer is, within the fluids element, create a "player collides with block" trigger. The "if get block at x y z" equals your liquid (use the XYZ to determine where the player is in relation to the liquid, so that this will only affect the player when they are under the liquid and not all the way outside of it) do attempt to override notion of event/target entity to get x velocity get y velocity + (number. Play around with it to get the "bouncyness" you desire) get z velocity.