Merms, they aren't unique or interesting in any shape way or form. They get devoured against bosses with area of effect attacks and get lost on their way home. Being able to have them as semi-permanent "bodyguards" isn't exactly a unique perk.
How about using those frog legs of theirs and having them jump and avoid damage? Wurt could use a simple piece of reed as a grass whistle and signal them to dodge attacks this way. Merms already have less dps then bunnymen due to kiting but die the same to things like bearger. I also don't believe it would make things like toadstool any less of a threat given their spore cloud attack. The player would also have to be more attentive thus reducing their own dps.