Note: Minify the command to avoid issues :)
How to use /summon {MOB} riding {MOB}
Killer Rabbit Boss
Rideable Wither
Cool Blocks like nether portal block,still water,mini TNT and more =) (not tested)
go 1000mph with a walking stick
TnT
Get cool minecraft banners in ONE COMMAND NO MODS!
Herobrine's Flesh