Pretty nice game demonstrating the concept of the game. Though i feel like besides spikes, you can add more deaths like falling off the world or having different types of weapons. And respawn points. You can randomly respawn into between 2 of your past self and nearly insta-killed.
That being said, the implementation of the idea is real neat and straightforward. I think this could do a fun multiplayer couch game, just a thought haha. Nice work!