Mob Placing in survival

One thing I love about minecraft is the ability to tell visual stories through builds/environments, with mobs bringing those environments to life. Specific to dungeon-making, I would like to record “Slain mobs” to an echo-shard related instrument, one per instrument to load onto an echo chamber/block that will project/generate the single mob recorded around a 15 block radius. They will not generate if they don’t have enough space. The block will not be affected by haste or mining fatigue and once destroyed, the mob will despawn. The mobs slain from here will not drop loot nor experience. Depending on how many echo shards are loaded onto it, it will respawn over and over. Creepers/ghasts generated from them cannot destroy blocks, and withers/ender dragons cannot be recorded. Mobs slain with specific armor/weapons given to them will respawn with those items but never drop them unless slain with the same instrument. It could be activated/deactivated with red stone. This would more freely allow players to design their own challenges/environments after the end of the game