Patches in an NPC encountered in Murkwater Cave. If you open the chest in his chamber, he’ll accuse you of stealing and then attack you. Fortunately, his attacks are simple, slow, and predictable, and you don’t even have to reduce him to 0 health to win the fight.
At about 40% health, he’ll surrender, and you now have the choice between accepting his surrender (stop attacking him for a few seconds) or continuing to attack until he’s dead. If you spare him, then talk to him, you’ll get another choice between “Forgive and forget” and “Some things can’t be forgiven.” Choosing the latter resumes the fight.
Generally speaking, you should not kill Patches in Elden Ring. If you do kill him, you’ll get a Spear +7 and some Leather Armor, which is a pretty good gain in the short term. But if you don’t kill him, you get so much more in the long-term. First of all, he’ll become a merchant, with better goods for sale than Kale at the nearby Church of Elleh, including Margit’s Shackle. You have to leave his chamber, then come back again for him to become a merchant.
Related: Murkwater Catacombs full walkthrough in Elden Ring
Secondly, if you kill Patches, then at least one key quest won’t spawn later in the game, and you won’t ever be able to get the Great Horned Targoth’s armor set, which is among the best armor in the game. Just don’t open his chest again unless you want to be teleported to East Limgrave. If this does happen, don’t worry. Ignore the giant bears and go to the Mistwood Outskirts Site of Grace by the road to the northwest.
