Just except the lightning and primedtnt, and golems, but it even spawns minecarts and every single mob witches, wolfs, sheep, squids, zombies, creepers, pigs, cows, chickens etc. So this is actually a mistake but I thought it was cooler than what I intended to do, I was just trying to spawn one tamed wolf but some how the command block spawned all of those entitys so to do it
set 4 command blocks up like the picture shows don't need to worry about the redstone clock yet. 
      So, in the very left command block type /testfor @e[type=Arrow] {inGround:1b} what this does it will look for an arrow in the ground for 1 tick like looking for something (the testfor part) looking for an arrow (@e[type=Arrow]) find it inGround for 1 tick.
      After it finds that it will light the comparartor up activating the 2nd command /summon Sheep it can be any entity you want maybe an Iron Golem type /summon VillagerGolem if you don't know how to summon it go to this link and type the ID in from the blog http://www.planetminecraft.com/blog/summon/ 
      So whatever you chose it's fine so after it gets summoned the repeater lights up and will activate the next command saying /tp @e @e[type=Arrow] this is simple it just teleports the entity to the arrow that you shot but this teleported every single Entity if you just wanted your entity to tp put this instead  /tp @e[type=VillagerGolem] @e[type=Arrow] and replace VillagerGolem with whatever entity you spawned in your previous command block. 
and the next command below the last command block is simply /kill @e[type=Arrow] this one is optional but I thought it would just help so if you want to spam these entitys it will get rid of the arrow so they won't be everywhere in your world.
But rememeber you'll need to activate this with a 2 repeater clock if you don't know how to do it here's how:
        Place repeaters right next to each other making them face opposite directions. 
Connect the corners with 4 redstone and then send 1 of the corners of redstone to connect to the 1st command block 
Like the picture shows Then add a lever to another corner and flick it as fast as you can then it should make a strobe effect to show that it's working. If that's too hard another way to activate it is place a redstone torch to light the whole thing up break the torch break a piece of redstone and replace it as fast as possible. 
                                              WARNING YOU'LL NEED TO PLAY IN 1.8 SNAPSHOTS FOR THIS TO WORK 
and if it still doesn't work copy the commands directly from this block using control+c and control+v