Adamantium Sarcophagus

You target a medium or smaller creature within range and summon a sarcophagus made of adamantium to attempt to engulf the creature in said sarcophagus. The targeted creature must make a dexterity saving throw or be encased in the sarcophagus where their movement speed drops to 0, they gain a +15 to AC, they cannot take any actions, bonus actions, or reactions, and they will instantly begin to suffocate. A willing creature does not need to make the saving throw. Once at the end of each of the creatures turns they may make a strength saving throw in order to attempt to break free of their sarcophagus. Other creatures outside of the sarcophagus may also attempt to make said strength saving throw on the target to help them escape. If the creature escapes by either succeeding a saving throw or by you losing concentration, then the sarcophagus disappears.