The word fiction casts a very broad range of beings to choose from, so take your time to give your pick and reasoning. For me, I have to say (and I know some will hate me for this) from JoJo's Bizarre Adventure, Golden Experience Requiem, the stand belonging to Giorno Giovanna from JoJo Part 5. Reasoning: GER's abilities include (Main Ability)- Can undo any action, no limits have been discovered yet on this ability. Like for example, if you want to kill GER and Giorno by going back in time and killing Giorno as a baby, GER simply un-does it. You literally cannot touch him, because he will just undo it, no matter what you do. You now never want back in time, and now you have a pissed off reality breaking being standing in front of you, which goes into the next ability. -If you are killed by GER, you are tortured for the rest of eternity. What this means is as soon as GER pummels you to death, you wake up in a completely new reality, and you are mere moments from death. You die again, how depending on the reality you woke up in, and wake up in a new reality. Then you do it again. And again. And again. This is your existence now, just dying forever with no end in sight. -GER has manipulation of biological life. What does this mean? Well it means 3 things: ~You can turn non-biological objects into living creatures (You can turn rocks into scorpions, paper money into butterflies, phones into frogs, hell even boats into whales if you practice enough) and you can turn them back whenever you want. ~Any physical harm brought upon your newly created life is reflected back upon the attacker. ~You can heal any injury on anyone and yourself. Can even bring people back from the dead to an extent. Yeah, I think its safe to say GER is thouroughly broken. You literally cannot kill him, because even if you do he just un-does it.