Swet (The Aether)

Swets are mobs found in the Aether. They are similar in appearance Slimes, but behave differently. Swets can spawn in any level, and attack both non-swet mobs and the player. They attack by capturing their victim inside of their body, jump high in the air, and then falling to the ground, which causes fall damage. Swets can easily be killed, and die upon successfully completing an attack. Most Swets are blue; but there are also gold Swets, which jump much higher, thus dealing more damage.

Uses
Blue swets drop in between one and four blocks of Blue Aercloud, gold swets drop in between one and four blocks of glowstone. You can also right click on a blue swet to ride it and null some fall damage while increasing jump height. To dismount, you right click. Gold swets cannot be ridden. Currently, if you right-click on one, it will vanish without a trace.

While riding in a blue swet, left clicking will have the effect of targeting the swet. So, if you attack with a sword while riding inside a swet, you will quickly kill it. Since you can take normal damage from other mobs and are unable to attack back, it is inadvisable to ride a swet into battle.

Trivia

 * Gold swets have a lower spawn rate than blue swets.

Video Wiki
Using Single Player Commands, it is possible to use Blue Swets as mounts. The problem is, you can't see anything except the Swet's innards when riding them.