The intended solution was to throw a sheep from the very top of the hill so it stops to the left of the nightmare, then destroy the nightmare, and then throw another sheep from the very top. The second one should bounce onto the floating platform, and you can complete the level by sliding down the hill yourself.
The easiest way to beat it might just be walking all the way to the other end and just stacking two sheep by the wall, lol. Thanks for playing!