I play Ranger Spikes into the Staging Area.
A bad guy pops out, getting Ranger Spiked.
I kill the bad guy who is Ranger Spiked.
Ranger Spikes go to my Discard Pile, or go back to the Stagine Area? I would normally assume my Discard Pile, but it does say "If unattached, attach Ranger Spikes to the next eligible enemy that enters the staging area."