So I've created a boss mob, whether it is naturally generated or spawned by the player, after some time it despawns, what can I do so that it doesn't despawn at all?

Thanks in advance

a method checkDespawn will fire. override it and see yourself. this one is useful if you want to do some checks and decide whether to keep the entity or remove it.

for simple cases maybe just override isPersistenceRequired and finito.