Now a good one, i never saw this in a game what i played,
Something like:
Sword of Sumonner
When you hit the enemy you have chance to summon a creature(nature) of certain lvl.
Or:
Sword of Dark Sumonner
When you hit the enemy you have chance to summon dark creatures of certain lvl.
And this sword can summon just a certain number of creatures, something like seven or something like this. Or maybe you summon all the time but can't control the creatures to follow you and they go to kill who they find. You just can control something like 7 creatures and the other go away.
