Mega Ring appears in 5 version groups since Generation VI, a Gameplay item in the Key Items pocket
PokéAPI item 739 of 2,223, Gameplay category, Key Items pocket
Effect, in PokéAPI's words
Mega Ring: “Allows the player’s Pokémon to Mega Evolve.”
Games
Mega Ring is listed in the text of 5 version groups, first in Generation VI
Game index by generation
IIIIIIIVVVIVIIVIIIIX
Named in
X and YSun and MoonUltra Sun and Ultra MoonLet's Go Pikachu and Let's Go EeveeSword and Shield