It's a power ring that makes green stuff.

Instructions

-Measure finger
-resize fingerhole in the ring (maybe whole ring?)
-print

Take the oath:
In brightest day, in blackest night,
No evil shall escape my sight
Let those who worship evil's might,
Beware my power... Green Lantern's light!

-put on finger
-fight evil

alternate use punch people in the face for a nice lantern mark on their tender pink cheeks