Quinn Conklin came up with this delightful idea:
Arrow of Summoning I
Aura faint conjuration; CL 5th Slot none; Price 132 gp; Weight 1/10 lb
[Description] This +1 arrow is painted with an oscillating pattern of colours and has black fletching. If it strikes a foe so that it would normally deal damage, it instead conjures a creature from the summon nature’s ally l list next to the opponent. The summoned creature attacks all nearest foes until it is killed or 5 rounds elapse and it is dispelled.
[Construction] Requirements Craft Magic Arms and Armor, summon nature’s ally I; Cost 70 gp.
The summoned creature can immediately attack, the arrow transforming into the creature, attacking and then falling away to an adjacent space to continue fighting.
I thought this was a great idea, so I wanted to do some variants of it: