Would it be difficult to add a second threshold to each mutation line that allows a player to choose the species of their mutation line? Maybe two or so for each?
I was thinking that just being a “spider” or a “plant” is a bit too universal. It works but there’s room to specialize. A fish character with electroreceptors could further mutate and become an electric eel mutant with electrogenesis, a mutation version of chain lightning CBM, or with a size increasing mutation could become a whale mutant and gain the ability to store things in their gigantic mouths. Likewise, a cephalopod character with bracing could further mutate into an octopus with the ability for a mutation version of the camoflage CMB and blinding slippery ink spray(works like boomer bile but on enemies) or someone with rakes mutate into a squid with tentacles that can do reach attacks at the same range of a spear if the mutation is activated.