Sounds nice, 4 hp is a lot, but it is only 50%
I'm not sure about the cost balancing. I think I'll just let Furball figure that out
50% chance of losing 3hp is not the same as dealing 1.5 damage to each opposing creature. Just throwing that out there.
Initial thoughts:
Don't know about if rockslide is balanced, stronger or weaker than it should be. Does 
need AoE CC like this? Play testing would definitely help.
Large Rockslide seems to be a bit UP in my opinion. It is 1 less 
than upped RoF, but the 4 damage (not that large of a difference from 3-4 hp as it is from 2-3 hp) does not seem to balance out the 50% of missing.
4 damage at 50% averages 2 damage per creature.
What makes this a tricky beast to balance is that, while it does less damage per creature than RoF, it can kill a wider range of creatures when it does hit.
The number of 4 hp creatures in game is pretty small though:
Cockatrice (unupped), Toadfish, Crusader, Flying VD (i think... need to double check that one), Flying Lobotomizer, Vampire (upped), and Psion (unupped), Aether nymph (unupped), GoTP (both), Silurian Dragon (upped), Elite Antlion (upped), Micro Abomination (upped) are the current 4 hp creatures....
,
So one way to look at it is this:
- Is 1 less + a 50% miss chance worth adding ~12 creatures to the list of those that can be killed in 1 shot over RoF's kill list?.
- I don't know all my weapon stats by heart so I may be off in my count by a few creatures, but I'd wager that the number of 4hp creatures is less than 10% of the creatures in the game.
There are lots of creatures that have 2 or 3 hp compared to those that have only 1 (where thunderstorm or UG is effective) an extra 12 creatures out the entire pool of upped and unupped doesn't seem that large (there are about 192 creatures in game right now, if you count all weapons, shards and consider upped and unupped versions distinct).
