Psychedelephant
Description: Imagine an elephant designed by a committee composed of Pablo Amaringo, Scott Draves, Alex Grey and David Normal after they'd been sleep-deprived for a week. It doesn't look much like that, but it looks even less like anything else.
Abilities: Psychedelephants have the same game statistics as a middling-sized dragon in your preferred rules systems with a few tweaks. If your dragons come in rainbow colors use a green one, it's the closest match. The usual physical attacks become stomps and gores and tosses for the same effects and damage. The creature flies as well (or as badly) as a dragon would, sometimes accompanied by the prodigious flapping of ears and sometimes simply by virtue of forgetting to obey the laws of gravity. Any other fancy movement abilities also apply, as do "draconic" senses - and it always has supernaturally keen hearing. Regardless of the dragon type you're using, psychedelephants have highly variable dimensions that permit them to comfortably squeeze into places one would not expect to find a more conventional elephant. Ten foot square rooms, for example.
Instead of a dragon's breath weapon, a psychedelephant can exhale a cone-shaped spray of vapor that acts as a contact hallucinogen and affects any living creature caught in the area. Well, unless you're wearing a sealed space suit or full hazmat gear or something. Where'd you get that stuff, anyway? This attack can be used once every d4 rounds and replaces the creature's physical attacks and (if your dragons do that sort of thing) spellcasting.
Creatures that fail to save against or resist the hallucinogen (treat as dragon breath, or poison, whichever is worse in your system) gain the "Tripping Balls" condition for 1d4+1 rounds unless magic or anti-poison effects end the condition early. Creatures that do save or resist successfully still have to roll once on the Tripping Balls chart on their next turn, but can roll two dice and pick which result to use.
Tripping Balls Chart - roll 1d6 once per round until condition ends
1. Keeping It Together, Man - Character may act normally this round.
2. Stay Cool, Stay Cool - Character can act normally this round but rolls twice for everything, taking the worst result of the two.
3. Bugsbugsbugsbugsbugs! - Character does nothing but stand there screaming and slapping at themselves this round. They drop anything they're holding 50% of the time.
4. Mellow Fellow - Character spends the round trying to convince everyone to stop with the negative vibes already. If they can make a convincing case for it through roleplaying they can test charisma or appropriate socials skills to get the fight to end for at least 1d6 rounds. Time seems to slow down long enough to make a brief monologue about peace, love, and understanding while attempting this. Elvis Costello may mysteriously play in the background while doing so.
5. I CAN DO MAGIC! - GM chooses the flashiest and/or most powerful spell the character can cast and uses it on a target of their choice - which may or may not actually exist. If the character can't cast spells they stand there shouting and waving their hands instead.
6. Bad Trip - Character uses the attack, spell, or power of the GM's choice on whatever target the GM chooses - which again, may or may not actually exist.
Behavior: While hypothetically intelligent and capable of speaking most languages, psychedelephants don't think like mortals do. They probably don't even think like immortals do. Predicting their actions is nigh impossible, but they do seem to enjoy using their breath weapon on people to see what happens, especially if those people are currently trying to murder one another. The best way to model their behavior from round to round is to roll a d20. The higher the result the more aggressive the psychedelephant will be, while lower results indicate a "playful" mood. Very low rolls would result in the beastie getting bored and leaving, usually with one last trumpeting blast of hallucinogens.
Possible Origins: These things definitely come from the Demi-Plane of Bad Trips, which is a cosmological suburb of the Plane of Madness. Or maybe they're literal pipe dreams puffed into being by trickster gods. But it's also possible they're just something you imagined after trying the house brew at the Don't Come Inn. Perhaps they don't exist at all and are just a hiccup in reality's OS.
Treasure: If you actually manage to kill a psychedelephant without it flying off, the body dissolves into a pile of iridescent powder that, if carefully collected, is worth the same total amount of XP that an equivalent dragon would have earned a party of murder hobos. Gaining those XP requires partaking of an appropriate proportion of the powder, usually through smoking, snorting, injection, baking into brownies, etc. If a PC would gain enough XP to increase their level, they will spend that entire level having to test on the Tripping Balls chart once per day at whatever point the GM finds most amusing. If they'd gain enough XP to gain two levels, they immediately ascend from their mortal form (ie die) and then reincarnate (as per the spell if your rules have such, or GM's choice of species otherwise) on the spot without the levels that triggered the overdose.
Systems that don't use XP (or don't award it for monster kills) will need some hacking so that the powder grants appropriate (or inappropriate) advances to skills, personal abilities, etc.
A psychedelephant that flees (or just wanders off) will generally leave behind 10% of the normal XP value of powder during their parting breath attack.
And because "predictable" is not a word that gets used for these critters, sometimes a slain psychedelephant will instead transform into a marble statue whose worth to the right collector or museum is equivalent to the minimum coinage value of its base dragon's horde. It probably doesn't weigh more than 5 tons in this form, and is considerably more definite about what size and shape it is than it was when still alive. Transportation issues may arise.