[ColBosch]

After consulting my collection...

Munchkin Cthulhu 2 is perfectly usable right out of the box. The only different mechanics between it and Munchkin Impossible are "Madnesses." Luckily, it includes the rules for Madness cards. Curses are just another name for Traps. Cards and rules that affect one CAN be used to affect the other.

Specific cards of note: Green Reaper is a Vehicle under Impossible rules. Spud Gun is (obviously) a gun.

Munchkin Pathfinder 2 is also perfectly usable. Factions are another kind of "character type" card like Loyalties and Classes. A card that affects Loyalties or Classes will not affect a Faction, and vice-versa. The other major mechanic is that of "monster types." You'll see this on many of the monster cards, between its level and the card title. Luckily, you already have the rules for these in Munchkin Impossible: they work just like the "...in Black" mechanic, but are specific for each type of monster. So you can play Goblins to add to combats involving other Goblins, but not Undead (unless they're Undead Goblins) or Monsters in Black. Again, Curses are just traps by another name.

Specific cards of note: This set includes lots of Guns! Have fun! Also, the Dagger of Doubling should be treated as a Knife.

Beyond those notes, if a card refers to something you don't have, just ignore that specific effect. For example, the Squidskin Boots from Cthulhu 2 mention Cowboys. Cowboys are a Class from The Good, the Bad, and the Munchkin...but you don't have any, so just ignore it.

As you can see, once you strip away the spy movie/eldritch horror/fantasy elements, the core mechanics of Munchkin are very consistent. This is one of the game's great strengths, and makes mixing sets a whole lot of fun. I hope this helps, and enjoy!