Roc's Ring: Jump when hurt
Roc's Ring L2: Jump when hurt, with hover boots
Flame Ring: Magic Book
Flame Ring L2: Magic Book but the fire creates 8 directions of fire weapons too
Lifesaver Ring: Like the Lifesaver Potion but you have to have it active
Equal Ring: Deals the same amount of damage to enemies as they do to Link when they touch each other (1 Link heart = 8 enemy HP)
Shield Ring: Magic shield
Shield Ring L2: Mirror shield
All-Terrain Ring: Slow Walk combos ignored
Conveyor Ring: Conveyor belts are ignored (possibly combined with the above ring)
Trap Ring: Ignore traps
Statue Ring: Ignore fireballs generated from statues
Heavy Ring: Ignore Wind EWeapons
Prism Ring: Create reflected LWeapons in 4 directions when hit with Rocks, Fireballs, Rising Fireballs, or Magic
Prism Ring L2: Create reflected LWeapons in 8 directions when hit with Rocks, Fireballs, Rising Fireballs, or Magic
Kick Ring: Can now kick bombs like in Destiny of the Oracles
Molotov Ring: Creates 8 fire weapons moving out from the center into a circle (like a Fire Wizzrobe) when Link's bombs explode
Molotov Ring L2: The 8 fires move until the edge of the screen
Bomb Ring: All Bombs, when placed down, are turned into Super Bombs.
Flamethrower Ring: Candle turns into Flamethrower (hold down to produce a stream of fire). Mostly only of use if the quest doesn't have damaging fire...
Asbestos Ring: Immune to own fire, if not already
Concrete Ring: Immune to own bombs, if not already
Defense Ring: Your usual Zelda 1 ring.
Vacuum/Magnet Ring: All enemy drops home in on Link.
Item upgrade rings: Gives you a next-level version of one item to use while these rings are active. You can make this work for any class of item with multiple levels like sword, bombs, bow, arrows, wand, candle, hammer, boomerang, cane of byrna, lens of truth, roc's feather, hookshot, din's fire, as long as you do not have plans for there to be more than one of the item in said class unless the ring is used. So you can't have an arrow upgrade ring AND silver arrows for instance because you could just turn on the ring and get them instead of needing to find them.
Here are some negative effects to put on overpowered Rings:
-Bait constantly spawned onto Link - use in an otherwise-baitless quest and make enemies like Bubbles and Darknuts hungry too for even more pain. Did you also know that Gleeok heads can be hungry?
-Bombs take twice as long to explode
-X weapon does half damage
-Sword and/or Wand melee and/or Hammer give you a Buzz Blob shock when you touch any enemy with them
-Chance that bombs are duds when "exploding" and do not do anything besides poof away
-Enemies are unstunnable
-Cannot walk against conveyor combos (possibly combined with the above)
-Enemies Always Return
-All enemy projectiles replaced with bombs, super bombs, or wind
-No enemy drops
-Cursed hearts/fairies, magic refills, ammo refills, and/or rupees (subtract what they normally add)
-All Armos combos on the screen are activated when you enter it
-Chance of every dungeon screen spawning one Wallmaster upon entry
-Chance of every dungeon screen spawning one L0 Wind Wizzrobe (Wind Wizzrobe with the HP of a Red Wizzrobe, so 8 HP or in other words 1/4th of normal) upon entry
-Every dungeon screen now has the Ceiling Master
-Some or all of these default enemies (Peahats, Leevers, Armos, Tektites, Keese) now spawn EWeapons like fire trails or statue fireballs, without even stopping to fire or anything. Consult Panoply of Calatia on how its global script detected enemies of a certain # (or name?) and spawned the fire trail on top of the Fire Keese
-Harmed by own fire if not already
-Harmed by own bomb explosions if not already
-Chance of every screen having a Zora on it (make this check to detect if there's a water combo first)
-Chance of every outdoors screen having 3 small boulders on it
-Chance of every outdoors screen having one large boulder on it
-Chance of every outdoors screen having Red Leevers on it. This could also be extended to certain "natural" dungeon screens that have dirt or sand on them, but any quest would need to keep this in mind for the walkability flags on those screens.
-Cannot use Ladder
-Cannot use Flippers
-Cannot use Potions (you'd think this wouldn't be easy to forget while you have the ring on, but it is)
-Enemy drops home away from Link (This is almost the same as them not dropping at all, but it's funnier)
I wish you could make an "Anti-Bait" ring, but I'm pretty sure you can't do that with normal enemies/Bait.