Playing as the clock girl (looked it up, Ouro Kronii) in Holocure. No collabs or special weapons allowed, so to make it easier just one level of +enemies turned on.
I got the achievement for that, for having haste over +100%, and winning as her (since the achievements were added).
Took max (so many extra points) on the items slots: +coins, lab coat (+exp if you don't get hit), +exp, Halu (more enemies who are also stronger, and you get some coins at the end as a reward), headphones with a 35% chance (at max) to ignore damage and knock all enemies back, and Knight Milk (bigger attacks, and you pick up xp, food, and coins from further away).
I did have the +haste, bigger weapons, and +5/10/15% attack per empty weapon slot stamps. 5 empty weapon slots when you don't allow special weapons.
Edit: Another dumb one today. Couch Potato achievement: don't move at all. It's a Vampire Survivors-like.
So, for a dumb achievement, I used a dumb character. Ceres Fauna has abilities that heal, and ones that do damage to a random enemy when you heal, encouraging you to just run into piles of enemies. Her weapon can't be aimed until it's maxed out , and just kind of floats around you. Then her special ability heals you and makes you invulnerable as long as you're in range of it (which, when you're not moving, and it starts centered on you...), which is great for making bosses accomplish nothing against you.
Took Knight Milk (more pick-up range, which is useful when you can't walk over xp to pick it up), breastplate (damage reduction, and chance to do damage back to the enemy), and nurse's horns (heal when you kill something) before finally getting my xp glasses. BL Books and Spider Cooking are great close-range AOE attacks, so xp falls near you. I also managed the "level 4 times in 1 second" achievement (time spent in the level-up menu doesn't count) when I upgraded my pick-up range and grabbed an xp magnet thing.
I grabbed wamy water for collabs, which work better if you can get to an anvil. The knockback there cost me some levels. I won anyway.