Making Instagibs Balanced

Recently, I've been thinking about what people complain about when it comes to balance in champions. One of the major ones is "this champion just 100-0 me and I couldn't do anything about it". It got me thinking, what if there was a way a champion could instantly (more or less) kill someone, but still be balanced. Here are some ideas I've come up with. Feel free to add your own input.

(R) Call of the Abyss: Champion drains their entire health bar to deal that much true damage to enemy champion. (ie. They die, but you die too)

(Passive) Cursed Idol: Champion begins the game with Cursed Idol. Allows Champion to use The Gift once per game. Item is consumed upon ability use. (R) The Gift: Champion unleashes the power of the Cursed Idol and consumes it to instantly kill target champion. (ie. You can only use it once)

(R) Death Trap Dungeon: Champion begins building a large intricate death trap invisible to the enemy team. Champion can leave the trap, but no progress is made while champion is away from it. Trap takes x minutes to build. Once trap is fully built the first enemy champion to walk into the trap is dealt (extreme amount) of magic damage/is killed. (ie instagib trap, but you have to stay in one area for a long time to use it)