The Maelephant is humanoid in shape with hands that appear oversized for its body and tipped with claws. It's head is similar to a small-eared elephant's head. It has a small mouth filled with tiny teeth, small red eyes, and a long, coiling trunk tipped with a long, thin spike.
Source: Planescape Monstrous Compendium Appendix AD&D 2nd Edition
Fiend Folio 3.5
The Maelephants are lower planes guardians. They are used by demons and devils to guard an object or area. Typically that agreement will be for 100 years. When not guarding something the Maelephant travels the lower planes with an intense urge to protect and guard although it has nothing of it's own to secure. If provided with large amount of living flesh it needs for sustenance the Maelephant will be greatly swayed to act an a guardians.
Once a Maelephant has agreed to protect or guard something they will not leave their post and will fight to the death. They never pursue beyond their boundary of guardianship. The Maelephant has an arsenal of abilities to deal with trespassers. From a memory erasing breath weapon to spell-like abilities.
Combat: The Maelephant is very high powered foe. Worth 10,000 experience in 2nd Edition.
-Defenses: Requires a magical weapon to be hit, can never be surprised, and never needs to roll for a morale check
-Claw/Claw/Trunk: The Maelephant has three attacks. Two claws that deal 1d6 damage and a slam with their trunk spike which deals 2d6 damage.
-Breath Weapon: The Maelephant can unleash a cloud of noxious vapor three times a day. The vapors requires a save vs poison or suffer complete memory loss. You completely forget who you are and all your abilities. It can be cured by a neutralize poison. The vapor does however require contact with skin. If more then 50% of the body is covered the opponent receives a +2 to it's saving throw.
-Charge: Can increase it's movement to 18 and get a +2 to all attack rolls for the first round of combat
-Crush: If both claws hit the opponent is held. The victim takes 1d3 crushing damage each round and it's spiked trunk attack automatically hits. To break free the victim needs to make a -5 strength check or the Maelephant needs to take 12 points of damage.
Spell-like Abilities: At will they can cast alarm, bind, entangle, gust of wind, light, true seeing, and warp wood. Three times a day they can cast blade barrier and polymorph others.
To me the most fascinating aspect of the Maelephant is the ability to erase player
characters memories. If you lose all your memories you are in deep trouble. Forgetting how to cast spell or use a sword could be disastrous.