Korski said it well but I'll try to add my two cents just to have some impact:Reopening the floor on Scald:
This CAP has been all about "overcoming an awful typing" and turning it into a benefit, but at every turn save the original decision to give it Dry Skin, we've been erring on the side of weakness on Mollux.
After we decided it wasn't going to have ultra-competitive alternatives like Drought in its moveset, we actually decided that meant that it had NO alternatives at all and its only usable ability for any sun team is now Illuminate . . . . ILLUMINATE. The only extreme makover we've given this pokémon has been to shove it into the tiniest niche in existance. Its stats are really only decent and its typing is terrible and, really we have given it very little to compensate for that. Outside of the rain, this pokémon is going to be outclassed at virtually evrey turn, and without at least scald, for example, Mollux i going to even get outperformed IN rain.
Fire is its only STAB with decent coverage, and it deals 50% damage in the rain, which outweighs the benefit of the attack being a STAB. Poison has laughable coverage, and without some sort of synergistic, custom, poison STAB, most movesets probably won't even USE the poison STAB. So what we are left with, in rain, where Mollux is supposed to excell, is a pokémon with its teeth kicked in: it has novel typing for a rain pokemon, but its got only moderately competitive stats and no real offensive threats in its movepool.
I know we agreed on its abilities, its checks, counters, threats, stats, etc already, but have you really stopped to think about the whole idea of this CAP yet?
So what did we do? We developed a pokemon who can't even USE the better half of his typing in his ideal environment . . . how have we exactly made Mollux's typing a strong selling point? we haven't done anything to accentuate his immunity to burns and poisoning via making him a wallbreaker, we haven't covered his most crippling weak-spot: being 4x vulnerable to the amazingly powerful, and nearly ubiquitous earthquake.The idea here is to create a Pokemon whose typing, while normally considered poor defensively and/or offensively, becomes a strong selling point of the Pokemon itself via help from an ability, stats, and/or movepool.
It seems like we are rather heavy-handedly making sure we avoid ANY accidental boost in Mollux's power, but we have no qualms about neutering him.
i.e. levitate as a secondary ability would have given mollux some diversity in his ability to negate one of his weaknesses. Arena trap would make him an utter wallbreaker and make his typing an amazing boon, and storm drain/water absorb would let Mollux function almost exactly the same, but be able to work outside of rain but, no, we got illuminate, not even mildly competitive abilities like poison point or flame body to solidify its role as a status inflictor, or limber or vital spirit/insomnia to solidify its role as being status immune, no, we got illuminate, and there was actually a movement that said that THAT was too powerful.
Now we have a chance to at least salvage what's left of this CAP in the movepool discussion, but, regardless of how terrible Mollux's offensive ability is in the rain, we can't give him scald as an actually usable attack since it hits certain pokémon too hard?
Well with everything that's happened so far in ability voting, Mollux is pretty much locked into a rain niche.... and in rain, his typing is STILL a handicap, but now it's an offensive handicap instead of a defensive one, but that is still something that NEEDS to be overcome by the definition of this CAP's Concept.
Have we really gotten to the point where our only options are: Go against the very core concept of this CAP, go against the counters/checks list or create an underpowered and increadibly niche CAP?
EDIT: as for the movement to create a custom fire STAB that ignores water's ability to weaken it by hitting waters neutrally and/or ignoring the 50% power decrease caused by rain. It has the potential to work around these problems, but it migh be clunky to balance. Flavor would be easy enough though, just name the attack "Grease Fire" since the LAST thing you want to do to a grease fire is throw water on it.