Nether Fireflies

Fireflies were meant to be added but sadly didn't make the cut because we can't let our darling frogs get into any harm

That got me thinking...FIREfly, their spark-like appearance...That's very convenient for the Nether biome!

"Regular" fireflies (orange/red) would roam around the fungi forests. Getting into contact would very briefly set you on fire and either kill the firefly or make it lose its spark temporarily. Anything that burns they could set on fire if coming into contact and frogs would die if they ate them.

Soulfireflies would roam around soul-sand valleys. They'd actually be flecks of souls that reside in the sand, roaming around freely. Perhaps these could be hostile-If hit they'd "fire up" and attack the player.

There could even be a unique type of frog in the nether that resides in the forests and eats these (thus being immune to the poisoning) and produces unique frog lights only obtainable there.