Since we're here: you should know that the elemental effects combine. It's not explained well inside the game, but if you put 2 status effects on an enemy it consumes them both to create a different one.

Electrocute + corrosive = poison (deals a % of max hp per tick, can stack; if you hit an enemy with something that rapidly applies electric damage with elemental chance while they're on a corrosive area, like the Crown Prince Gas Grenade, it will destroy their hp bar very fast)

Electrocute + fire = explosion (good for dealing with many enemies at once ofc)

Fire + corrosive = charm (a lot of games have this kind of effect, in Gunfire Reborn it has a bit more strength due to the really strangely long duration)

Some occult scrolls give you 100% chance to inflict the elemental effects. For example after switching weapons. If you get this, it can be disgustingly powerful with a shotgun or SMG while the enemy is continuously being applied with another element. It will create a stack of the debuff for each hit.

The vaults on each level can contain more than one reward. The ones where it's just a parkour challenge or the boulder traps always have 2 chests, you just have to look for the second one after you reach the end.