Honestly, a huge +1 from me. I use to use snowman a lot back in the good ol' dayys, mostly due to its ability to give slowness to others when their in your snow territory. This permitted me to rush people and was an overall good melee kit. Fast forward to now, it seems to be just a weak kit overall due to the updates and addition of new kits. Though that's not entirely the reason behind its weakness rather there are other melee kits that are way stronger such as creeper and wolf. So I'd say adding in ice prison and seeing how it goes will bring fourth a nice balance to the kit, in my opinion the prison should be at least 3 seconds with a 10-20 seconds cooldown, the player that is trapped should not be able to escape until the prison withers away. Additionally, just like DOM, there should be a hole at the top where the snowman can come in (well anyone can, but that's the essential idea of it).