I think I've found it: Irontooth, an elite level 3 goblin, backed up by a level 3 kobold, two level 2 kobolds, three level 1 kobolds and ten weaker kobold mooks. The party at this stage is level 1.
Irontooth has 106 hit points and an AC of 16. He attacks +8 vs AC for 1d8+4 damage, and can attack two targets per round if he doesn't move. Any time he's on half hit points or less, his attacks deal an additional 1d10 and he heals 5 hit points at the end of each turn.
That's 6-22 damage (average 14) against one or two targets per round. He hits the pregenerated dwarf fighter 60% of the time and on average will kill him in two hits. The fighter hits him 50% of the time dealing 2d6+3 (5-15, average 10). On average, the fighter's basic attacks only just keep Irontooth's regeneration down, which conveniently keeps Irontooth's damage up.
Supposing the rogue makes it past the sixteen underlings and flanks Irontooth, he hits 70% of the time with Sly Flourish for 1d4+7+2d8 (10-27, average 18). That is to say, that once bloodied it takes the fighter and rogue working together an average of just over 4 rounds to kill Irontooth, while it takes Irontooth an average of 3.69 rounds to kill the fighter, assuming the fighter is on full hit points when is the goblin is bloodied and no other minions attack the fighter.
