• claw +13 (2d6+6)
• bite +10 (2d8+6)
• giant mace +9 (3d6+6)
SP sweeping blow, stench, regeneration, immune to critical hits, immune to mind-effects, immune to poison, vulnerable to fire
The Ogre-Troll stands 20' tall, and will strike fear into the stoutest hearts. Beneath it's amber skin is a highly dense, mossy substance, with no internal organs, nor muscles, nor bones whatsoever. Its meager intelligence tells it that it exists only to feed, and it will feed on anything, starting with living animals — including humans and demi-humans.
When it hits with a claw attack, if it exceeds the target's AC by 10 or more, that target is swept up in the thing's mighty swing and tossed 2d30 feet away, taking 1d6 damage if swept more than 10 feet.
Alternately, when it hits with a claw attack, it can pick up the target instead of doing full damage (reduced to 1d6). It can then use it's bite attack to begin eating them, needing an attack roll to get an effective chomp. Escape takes an Agility (Dex) Check or a Strength Check vs. DC 20.
The behemoth has a frightful stench, a concentrated odor of rot. Anyone within 30' of the creature must make a Will Save vs. 18 or suffer with all dice rolled one step down the Dice Chain (d20 > d16 > d14, etc.). After 3 rounds, one can adjust to the horrendous smell and overcome the effect. But if re-encountering the creature, the stench effect begins anew.
The Ogre-Troll regenerates hit points at a rate of 2d8 per round, at the end of the round. if reduced to 0 hit points, this effect continues. Only if killed by fire or some very extreme means does the regeneration stop.
The creature's density and lack of vulnerable organs makes it immune to critical hits. It's lack of a true brain make it immune to mind affecting spells and the like. Poison does not affect it.
On any round that it takes fire damage, it's regeneration is reduced to 1d8, but it cannot recover the damage from the fire in this way.
[Presented as an option for the One Page Dungeon Contest entry The Umber Woods from 2016]