These are completely resistant to blunt damage, which means any blunt damage weapon wont do anything to it. The crabs on the floor above are completely resistant to slashing, skeletons above that are completely resistant to piercing, and weapons on the top floor are completely resistant to magic.
We suck on these, will do 0. The only saving grace we have is to 1) Chi Blast or 2) Get a pair of Vampiric Claws.
With Vampiric Claws you WILL be able to do some damage, but your kick attacks will do 0 and your weaponskills will do 0. I also believe your counters will do 0 (I'm not totally sure, I don't remember totally).
However on the remaining floors after the Amoeba we're golden and can wear our usual weapon.
Very weak to daggers and ranged attacks (piercing) with very high WS damage. The boss mob on this level is another slime type. I hit him for 3400+ slug shot (O-Bow, DS bolts, normal equipment). This first floor is very easy and quick. Bizzaro mobs that have very extreme weakness / defense but it's not as simple as just the opposite of what you would normally see on the outside.
Found in Apollyon SE. Like all other mobs in the area, these are weak to what they are normally strong against. As strange as it might sound, meleeing these slimes will take them down very quickly. All types of melee seemed to work, and WS's frequently broke 1000 and even 2000 damage. Predator claws also hovered in the 1500-2000 damage range. Watch for fluid spread, however, it is very dangerous and can one-shot mages without stoneskin.
Think SE's running out ideas for monster names? :P Let's just hope this thing doesn't latch onto your face and suck the life out of you. Get your power bombs ready, everyone!