The Almiraj or Al-mi'raj is a monster that originates from Arabic mythology and is the source of several Arabian poems. In appearance, it resembles nothing so much as a large, brightly colored (the traditional description features saffron-yellow fur) rabbit with an onyx-black unicorn horn growing from its skull. Despite its innocuous appearance, the almiraj (also known as Mi'raj, Mir'aj or just Miraj) is actually a vicious predator; swift and agile, it brutally attacks anything that draws too close, goring them to death with its horn and then eating the remains. In fact, this gluttonous carnivore can devour creatures several times larger than itself.
Basically, the almiraj is one of those concepts that is simultaneously stupid beyond belief, and yet crazy enough to be awesome. As such, it has popped up in a couple of roleplaying games.
Dungeons & Dragons
The almiraj first crossed the paths of Dungeons & Dragons in the original Fiend Folio, a secondary Monster Manual sourcebook for Advanced Dungeons & Dragons 1st edition. Here, it was... nothing particularly special. It was basically a bad-tempered bunny that could stab somebody with its horn once per round, doing the same 1d4 damage as a dagger. The most unusual thing noted about it was that the young could be tamed and the creature could potentially make a good companion.
The almiraj would later reappear in AD&D 2e, in the Monstrous Compendium Appendix Fiend Folio sourcebook. Here reputed to be an experiment of Krynnish gnomes gone horribly right, the almiraj picked up the nickname of "blink bunny", because it now had the inherent ability to randomly teleport all over the place. They also gained a variant; the psionic almiraj, whose access to the Sciences of Detonate and Telekinesis paired with the Disciplines of Control Flames, Control Lights, Control Winds, Levitation, and Molecular Agitation earned it the in-universe nickname of "Bunny of the Abyss".
Sound like overkill? Well, imagine being attacked by a whole herd of pissed-off rabbits with daggers on their heads that keep randomly teleporting around. Now imagine that 1 in 10 of those little bastards is using psionics to throw shit at you, lift you off of your feet, throw fireballs around, and either set your gear on fire or make it explode as you're wearing it. They earned the name fair and square.
WoTC did not think very much of the almiraj, and mostly left them to rot. In 3rd edition, "The Tome of Horrors", a third-party sourcebook by Necromancer Games aimed at adapting the critters of the Fiend Folio, converted the 2e almiraj to 3e mechanics as accurately as they could.
Indeed, WoTC wouldn't touch the almiraj until 4th edition, where the blink bunny resurfaced as "The Garden Variety Almiraj"; this version went back to basics and focused mostly on being a quick and nimble skirmisher that tried to stab people to death with its horn. It did have the unique ability to immediately burrow its full speed if it missed an attack, allowing it to effectively teleport around the battlefield without directly being a teleporting monster.
But, evidently, Chris Perkins and the other WoTC members who worked on Tomb of Annihilation have a soft spot for the almiraj, which returned to print at last as an official D&D monster in the aforementioned 5e adventure. This version of the almiraj has gone all the way back to its roots, and is once again a quick and agile carnivorous bunny that disembowels people with its horn. In fact, it's now officially considered a possible option for a wizard's familiar, because why have a bunny in your hat when you can have a murderous meat-eating bunny instead?
Almiraj gravitated to Pathfinder in the 4th Bestiary, and took on a much darker tone than they had in D&D. The Pathfinder version of the almiraj has a horn which functions as a magic weapon... and which also petrifies anything it kills. This forces the almiraj to focus on maiming attacks when hunting, using its horn to inflict terrible wounds or crippling damage so that it can then eat its victims alive. It's also unusually responsive to witch hexes. The Pathfinder almiraj can be taken as an Improved Familiar by a caster of at least 5th level.
In Castle Falkenstein, the almiraj - or the miraj, as they call it - is one of the magical creatures that appears in the Curious Creatures sourcebook. This version of the almiraj is quite docile by nature, but also strange and magical; it feeds on "soft" metals, like copper, tin, bronze, brass, gold and silver, and uses a horrific scream attack to scare away potential predators.