Here is the full list of all 14 Oblitus achievements.
Reach the Caves area.
Beat any overworld boss.
Kill any boss without getting hit by it.
Kill an enemy with your spear offscreen.
Kill 5 enemies.
Beat the Final Boss.
Beat all bosses in one run.
Collect all artifact pieces.
Reach true ending.
Unlock all enchantments and equipment.
Unlock the Underworld.
Find all spear upgrade plants in one run.
Burn all villagers in the Forest while your spear is on fire.
Beat the game in 25 minutes.