Which skills are considered to make the game a lot less challenging? I know Deadly Gift is one are there others?

That scorpion trap release make the game almost too easy.

In addition:
- polymorph is infinite duration instead of whatwas intended (there are also some traps on containers cursing the player, so save&reload is necessary)
- the dead knight summon (summon demonic aid) can kill a certain NPC, thus maing the game unsolvable
- from resurrection you can make infinite exp

Note:
- scorpions don'tjust make the game way too easy, they can at a placeresult in the same gamecrash you get you try freeze bosses