Go into creative, spawn a command block (/give name 137), then put this command in it:
summon Minecart ~50 ~50 ~50 {Riding:{id:"EnderDragon"}}
It will spawn an Ender Dragon a little bit away with a Minecart on its back you can ride. Sorta fun to do on AMPLIFIED world type, since the land goes so high the dragon HAS to fly through it and make paths, unlike in the normal generation where it flies harmlessly over the land. Of course, while riding, you're blinded inside blocks.
Edit: For once, this guy's list isn't actually good:
http://www.reddit.com/r/Minecraft/comments/1ls56m/minecraft_snapshot_13w36a/cc26jaaIt seems most of their list is based off rumors before the release, as he marked off biomes as hearsay and put incorrect information based on pre-snapshot posts, such as Weighted Pressure Plates not working with items anymore, which is odd considering they are still entities so if anything they're expanding from items to all entities.
Edit: Screwing with different tests.
Pig riding invulnerable, non-despawning Bat:
summon Pig ~0 ~0 ~0 {Riding:{id:"Bat",PersistenceRequired:1,Invulnerable:1}}
EnderDragon riding invulnerable, non-despawning Bat
(Warning: Bugs out into the distance FAST. Always happens unless you use an unshiftable entity such as a minecart or boat):
summon EnderDragon ~0 ~0 ~0 {Riding:{id:"Bat",PersistenceRequired:1,Invulnerable:1}}
Pig riding invulnerable, non-despawning Green Villager:
summon EnderDragon ~0 ~0 ~0 {Riding:{id:"Villager",Profession:5,PersistenceRequired:1,Invulnerable:1}}
summon Pig ~0 ~0 ~0 {Riding:{id:"Villager",PersistenceRequired:1,Invulnerable:1,ActiveEffect:{1:{Id:2,Amplifier:6,Duration:1000000,Ambient:1},2:{Id:8,Amplifier:128,Duration:1000000,Ambient:1}}}}
Pig riding invulnerable, non-despawning, unable to Move or Jump Villager:
summon EnderDragon ~0 ~0 ~0 {Riding:{id:"Bat",PersistenceRequired:1,Invulnerable:1,ActiveEffect:{1:{Id:2,Amplifier:6,Duration:100000,Ambient:1},2:{Id:8,Amplifier:128,Duration:100000,Ambient:1}}}}
EnderDragon riding invulnerable, non-despawning, unable to Move or Jump Bat:
summon EnderDragon ~0 ~0 ~0 {Riding:{id:"Boat",PersistenceRequired:1,Invulnerable:1,ActiveEffect:{1:{Id:2,Amplifier:6,Duration:100000,Ambient:1},2:{Id:8,Amplifier:128,Duration:100000,Ambient:1}}}}
PrimedTnt riding a Bat:
summon PrimedTnt ~0 ~2 ~10 {Fuse:90,Riding:{id:"Bat"}}
EnderCrystal riding an EnderDragon (If this thing is so badass, why doesn't he do this by default? xD):
summon EnderCrystal ~0 ~5 ~0 {Riding:{id:"EnderDragon"}