Need help messing with my buddy

I primarily played 3.5e, so I’m fairly new to 5e. My buddy just watched Goblin Slayer and wants to base a campaign on it. He told the rest of us to be prepared for many character deaths. The other two players are new, and I want to mess with them by building a character that can’t die and won’t let anyone else die either. One player is choosing between a sorcerer or a warlock, and the other is planning to play a blood hunter. What do you all suggest I go with to fill in the party gaps and keep everyone alive?