Ring of Pain

Firebeads are the red fireball enemies that follow you until they explode. A firebead has only two HP and explodes after one turn when they stand next to the player. The turn before a firebead explodes you see it lighting up and becoming bigger and smaller.

Easiest way is to find the "Hex" scroll ("Transform target into a frog", blue rarity) and keep on to it until you encounter a firebead. Once found, just cast the scroll on the firebead when it is one turn away from exploding and it will turn into a frog.

Alternatively, you can use the scroll Seed of Chaos to devolve all enemies in the current room. Just make sure there is a firebead that is one turn from exploding when using the scroll. Credits: induvielgamer

Note: The achievement doesn't unlock when you use the scroll on poison beads (the green explosive enemies). Credits: Jazz Apples

Note 2: The achievement DOES unlock when using the scroll on huge roaming beads that you can encounter in later rooms. Credits: ABoTxBagel