This is not a post about lore, he went to the dungeons of Fear and Hunger and came out alive, he deserves to be OP, and I like him as a character.

Gameplay-wise, I felt like picking him (or even killing him and taking his skills) completely trivialized my experience, something that is, in my opinion, counterintuitive to the design philosophy of F&H. If you start with him, you can get an Iron Spear to start, giving you access to Piercing damage, which is hard to get, you get a damaging spell, Danse Macabre, a Chac Chac, a Skin Bible of your choice, 25 HP as if he needed it, even an early Small Thing's Amulet if you do the full text adventure (which I'm not gonna criticize, you should get a big reward for going through the trouble, but it's already on a stacked character).

Let's talk about the problem children in the room: Spice Forge and Danse Macabre.

Any of the Spice Forge options could be its own skill and I still would pick them all. First spells completely break the action economy of the game (when it doesn't completely break the game and lets the enemy take a free turn for some reason) letting you fight usually tough and punishing enemies without consequence. Greater spells basically remove the cost of spells if you have a betel stone, whereas I had to use three accessory slots with my other playthroughs to achieve the same effect. Double spells are by far the weakest and most situational, which is insane to say since it's literally doubling your damage output, granted RNG is on your side.

Speaking of damage output, Danse Macabre. Can you survive one turn? Do you have Black Orb? Congratulations, you win. Literally how my fight with the final boss went. It scales waaaay too fast. If anything needs to be changed, this is it. It costs nothing, you can start with it, and first turns are usually setup anyway.

Now I have no problem with becoming OP in F&H games, I don't even have a problem with being able to oneshot bosses, but it needs to take proportional effort. The first game has you run all over the place, scavenging for crumbs of power piece by piece to stand a chance. Abella can build up to Meat Grinder. Marcoh takes multiple turns stacking buffs on himself. Hardened Heart costs 99 coins. All you have to do to be OP as O'saa is pick O'saa, and I do think that's a problem.

Now I'm not gonna offer options on how to fix it, I'm not a game designer and know my limits, but I have nothing against O'saa being the big powerful mage pick. In fact, it was a lot of fun running around one-tapping enemies with free Black Smog and getting free first turn blood golems. I understand the design philosophy behind his skillset, but his numbers just don't make sense in this game with very frail torsos and no post-death attacks like the first one. Everyone else's skills feel like utility, or set up, or pieces of a build, but he is the entire build.