The Combine Ring's icon on a monitor's screen is represented by a dark blue ring. When obtained, this power-up causes the Rings the player hold upon taking damage to merge together into larger Ring(s) as they are dropped. Should the player then re-obtain such Rings, they will regain Rings equivalent to either the entirely of the Rings they lost or just a portion of it, similar to a Super Ring.
The Combiner Ring first appeared in Knuckles' Chaotix. When picking up the Combine Ring, its icon appears to the bottom of screen and stays there until the player receives damage. At that point, the player will only lose a single, larger Ring which will return all the Rings the player just lost after taking damage. If the player does not obtain the large Ring within a few seconds though, it will burst into the usual shower of regular Rings when the player takes damage.
In Sonic Mania, the effect of the Combine Ring is slightly different compared to the effect in Knuckles' Chaotix. Upon picking it up, no icon shows up at the bottom of the screen. Also, instead of one large Ring being dropped upon taking damage, a few large Rings are dropped, each returning a small portion of the original Ring count.
↑"Combine Ring is silver instead of gold. It combines into one all the Rings you lose if you touch a Badnik or hit dangerous terrain. If you grab that one Ring, you regain all the Rings you have collected before." - American instruction manual of Knuckles' Chaotix, page 18.