There was a thread somewhere in which the damage caused by the slimes in frogger from Naxx25 was being discussed - couldn't find it but last night I decided to give it a test after we'd beaten Patches.
I was in bear form, raid buffed to 42k health and I'm a Tauren - the slime did nature damage, inflicted 19k and change and I resisted 9k and change, so about 30k damage total - this is from a direct hit, me walking straight into the slime.
No one was near me so no clue what kind of additional damage the aoe would do to others and I only took one hit so its possible the slime can inflict more.