Today I'm going to tell you some cool '/summon' commands that you can use in-game, these work on singleplayer and mostly multiplayer too, so you can do this sort of stuff with your friends too. 

First off, do you know what '/summon' does, if you do then just ignore this paragraph, if you dont know about '/summon' then keep reading. Okay, the '/summon' command is basically a command version of a spawnegg - but it does alot more, and you can add your own modifications to spawning animals. In multiplayer, its abit like the '/spawnmob' command; except '/summon' yet again has more choices.

Right, a small example of what you can do with '/spawnmob' could be to create a 'jeb' or 'dinnerbone' sheep without using anvils and name tags. All you need to do is the command below.

/summon Sheep {CustomName:Dinnerbone} or /summon Sheep {CustomName:jeb_}

Now, there are more things you can try out. I've added a-few more commands for /summon below for you to experiment with.

Skeleton Horse = /summon EntityHorse ~ ~ ~ {Type:4}
Undead Horse = /summon EntityHorse ~ ~ ~ {Type:3}
Huge Wither-Boss =  /summon WitherBoss ~ ~ ~ {Invul:10000}
Upsidedown Huge Wither-Boss =  /summon WitherBoss ~ ~ ~ {Invul:10000,CustomName:Dinnerbone}
Wither-Boss spawnegg = /give {player} minecraft:spawn_egg 1 64 [NOTE: CHANGE ID's FOR DIFFERENT MOBS]
Special Effect Witch with Bow = /summon Witch ~0 ~1 ~0 {Equipment:[{id:bow,tag:{ench:{id:48,lvl:5}]}},{},{},{id:chainmail_chestplate},{}],ActiveEffects:[{Id:22,Amplifier:1,Duration:999999},{Id:8,Amplifier:1,Duration:999999}]}

That's all for now. I hope you have fun messing with these commands!