8 Video Games That Made You Regret Killing Bosses

There comes a point in Chrono Trigger where players are confronted by Magus at the North Cape, and he provides the option of battling him in mano a mano combat.

Accept Magus' offer and, as Frog, you'll take him on in a tough boss fight, after which Magus will perish.

However, you're much better off turning down the offer, as refusing to fight Magus will instead result in him joining your party. 

Given that Magus is a solid fighter and has plenty of interesting dialogue throughout the rest of the game, it's absolutely worth keeping him around.

Furthermore, you'll avoid slogging through one of the toughest battles in the game, so that's neat.

Granted, you can't really be blamed for throwing down with Magus in the first place, given that his undeniably adversarial tone leading up to the fight offers little suggestion that he can be brought on-side.