The compacted ferocious ring is a ferocious ring that has been condensed with a teleportation compactor. It provides the same teleports as the normal item, but can hold 100 charges. It can be recharged by using more ferocious rings on it.
Rather than compacting a ferocious ring, one may prefer to fuse them into a full slayer helmet (or higher level variant), by purchasing the ability to do so for 500 Slayer points.