My main problem is the spell slicken. It's ridiculous that it allows you to get drakes and slimes prone. How does a dragon who is flying slip on an oil spill. Another is knock down, seriously how do you knock down a ghost who is levitating above the ground. Even their animation when they do that is silly. I know it would make some classes underpowered in certain encounters, but it would add to the atmosphere. RPGs are about fighting monsters, not walking stat blocks. If a creature is flying then players shouldn't have problems accepting that ground-based abilities won't work on him. 

This is already discussed here:

 

http://forums.obsidian.net/topic/75718-no-immunities/

 

And yes, this is a very bad combat mechanic.

I see, thanks. I'll move to the other thread then.