5 headed hydra looks good, breathe fire and 5-10 attacks a round. Fast healing of 15 (ogre mage is regen +5). You would lose in some areas, but I think the hydra would be a good bet.
troll wouldn't work as it has 6HD, but even so... the gains wouldn't be that great. Same regeneration, and while the troll is better it's not THAT much better.
another idea might be a phase spider. The stat's aren't that much better, but it gets etherial jaunt as a free action and has poison damage. It's attacks get the same bonus, but do less damage. But it bites and runs. If the party has few force type spells and can't cast true seeing...
a rust monster has 5HD. If the ogre isn't afraid of being killed in one shot (AC 18, HP 27), he could do some nasty damage to weapons and armor before going back to ogre.
troll wouldn't work as it has 6HD, but even so... the gains wouldn't be that great. Same regeneration, and while the troll is better it's not THAT much better.
another idea might be a phase spider. The stat's aren't that much better, but it gets etherial jaunt as a free action and has poison damage. It's attacks get the same bonus, but do less damage. But it bites and runs. If the party has few force type spells and can't cast true seeing...
a rust monster has 5HD. If the ogre isn't afraid of being killed in one shot (AC 18, HP 27), he could do some nasty damage to weapons and armor before going back to ogre.