Make use of the rows of blocks marked with a skull at each end. Knock out one skull block and all of the middle blocks, wait for unicorns to fall into the gaps and knock out the other skull block. This will cause the whole row of blocks to fall, killing all unicorns in the holes and below.
Use your hammer to briefly stun a pursuing unicorn, allowing you to escape.
If a unicorn is chasing you up a diagonal ladder, push the top of the ladder away when you reach the top so the unicorn ends up on a different platform.
Blue unicorns are quite dangerous, and after a certain amount of time they duplicate themselves, so kill them as fast as you can if you don't want to be outnumbered!
You can kill a unicorn on the same level as you if he is standing on a block when you hit it. The unicorn will fall and you will be awarded the same score as if you had knocked the block down onto the unicorn.
If a unicorn is filling a hole vacated by a block, you can hammer it to knock the unicorn down to the next level. Note you CANNOT do this to a blue unicorn.
Wait until all unicorns are as close as possible before collecting the cross to turn them into Alphamonsters, giving you more chance to kill more of them.
You can fall from any height and will not die so jump down through gaps to avoid unicorns.