Ring of the Summoner (5e Equipment)

Ring, very rare (requires attunement by a spellcaster)

This ring strengthens the creatures that you summon through magic. While you are wearing the ring, you have advantage on concentration checks to concentrate on spells that summon creatures. Additionally, when you cast a spell that summons a creature, such as conjure celestial or conjure elemental, the creature appears with 2 additional maximum hit points for every hit die it possesses, and it also gains a +2 bonus to AC, ability checks, attack rolls, saving throws, and damage rolls.