Cleric is absolutely 100% mandatory if you're trying to do green quest item runs.
I haven't been able to test this but I'm curious if the cursed candle or other means to allow you to remove cursed items can be used to cheese green quests by just unequipping the quest item until you get to the event that requires them.
i wouldn't say cleric is mandatory EXACTLY, but 99% of runs you really should take cleric, or get lucky rolls with druid, or both tbh druid's actually pretty synergistic with good rolls, because you only find out if you have a team broken enough to not need them generally mid-late run. you can start off with like a good hunter crit start then get jack shit but the worst possible minion options then a trap on basic attack, and it can happen to multiple classes. it's just a good failsafe. i dunno where "im jon snow and i don't need no cleric" extends to but i'm not fuckin taking 4 fighters or some shit to the rift+ difficulty wise unless i have farmed sets and near perfect mutations on 7 stat cats or i'm just in the "this is jackass (sponsored by meowmix)" stage imo. especially before butch is capped.
i'd also like to chip in on classes, though i'm not super knowledgeable about everything
collarless- shit by design, but would recommend people try to eventually get through caves and boneyard with one at least, you get metronome (random spell use) and skill share (really interesting because it upgraded affects it's children always getting it's second passive) abilities that can roll on all cats
fighter- tbh i'm kind of disappointed with them later on, they're good and all but a lot of their shit is just very finnicky and i dunno, i know they have the POTENTIAL but i always feel a lot safer and better with damn near any class, tank with thorns and knockback, monk with bruising, butcher etc. monk in particular i feel like is just a lot less finnicky and a lot more guaranteed to get a ability combo in a run, be less squishy, and more adaptable. i honestly feel like they're a bit overrated because their "well i know at least they'll always be useful" i hear people say is not them, it's the monk, especially later on when dumb muscle becomes naturally harder to use
hunter- i wouldn't say they're op exactly, especially with future reflect bullshit, but they're one of the main classes that's basically mandatory, or doesn't have another replacement or substitute. it's basically the only class that's the easiest to ensure bosses aren't marathons, and any boss that takes multiple tiles being hit by scatter shot with high crit and passives get shredded tf up. double shot etc shreds single targets, if you have a monk or other class that applies bruise, and if you get something like horse blinders on them, you're really ready to go. especially if you can find ways to pump their con or survivability just to be safe.
mage- i like them but they really are just gimmicky af. i heard about a meme where they can just have absorb and that basically be it and eventually it happened to me, they can get cool combos and damage but they usually wind up being shit ranged damage or shit cc
tank- underrated imo. thorn stacking on a con/pincushion tank with backup is one of the easiest ways to play most of the game, and knocking shit into walls taking thorn damage, the taunt passive, the guaranteed con etc. i haven't taken them in a while because using fighter/monk/butcher is a bit more variety but they "just work", especially if you get stuff like stone orbit and pet rocks online with it etc.
cleric- very good, heals are nice in a bind or for winning by marathon, and also has tons of buffing abilities. chosen warrior/grace spam on a hunter etc. also do decent damage if needed. there's not really a reason to take someone else instead for their slot unless you just want to, or want to say you did. i mean you can give your dps 2-3+ more attacks and near invulnerability, burst healing for others, or you can take a thief or some shit, which way western man
thief- i dun fuckin like it. ignoring shield is nice for robots in the lab and bunker etc, but so is hunter. tbh thief in particular feels like it can be replaced by several classes just equipping items, like slapping status effects on hunter etc. get cats to higher stats and high speed is not very impressive, and can even be a downside because you can't buff them before they attack. just very meh. i'd literally rather have a jester.
necromancer- early they're good but i dunno how i feel about them. can't take them to boneyard or a couple other zones like with bumblefoot without it most always being a pain in the ass. some of their most powerful stuff also requires more cheese shit like leeching disposable friendly units etc, their projectiles etc also get fucked in the future. when they work they're fun though, and have built in self sustain, and soul link is probably one of the best status effects in the game under certain conditions (if you ever can roll the shit), they're just kind of finnicky to actually have necro abilities or leech abilities instead of only rolling a mediocre hybrid set. BUT they usually never feel like total shit, and their range is very comfy to avoid a lot of shit at melee range while also being tanky af
tinkerer- i really want to like it, but by act 3, it almost feels like intentionally handicapping yourself without very specific abilities, and even then. the mech suit is very fun ON PAPER, in reality it's like a 4 tile 16 hp big piece of shit that also blocks/damages all your cats and on destruction kills your cat. your rng weapon without tech ability is literally limited to shit like a stick, paper ball, or battery, and you can find no tech abilities a run. they have low stats and require very specific abilities and shit like full metal armor on hand to do stuff. fun at times but very fucking meh.
butcher-alt tank imo. with meat passive and some abilities is the tankiest unit in the game imo. works really well if you can get a cat with very high movement beforehand to offset the penalty. vurp also has some very interesting mechanics, like you can drink a full water bottle, throw it, vurp, and have a half full water bottle returned. makes dealing with fire/desert much easier. stuff like running to food items guarantees tankiness. their base attack also can target ne, nw, sw, and se, which feels amazing, and their guaranteed pull. monk and butcher feel really good to just work by default without needing/really wanting shit every time.
druid- tbh a long time i thought they were the biggest piece of shit, but they just require specific rolls. you can get stuff like safety dance which when upgraded gives all allies on the field 2 shield for 5 mana, you can get refreshes on your basic buff/heal spell each song spell, and you also get the crow every fight, which when you pump druid's con, acts like a free tank, and can do 8+ damage and has a knockback and movement spell. a lot of his shifts are dogshit though, like raccoon is only useful if farming alley or something. there's a lot of surprising synergy with classes though, even with cleric. cleric and druid both pump tf out of dps on units while increasing survivability so it generally never feels like you're losing dps, just making your classes you're wanting to do shit do *more* instead of taking a fill. you can also take items which increase healing power for druid and imo with that and good rolls, or with cleric passives inherited, druid>cleric, just doesn't burst heal very good
psychic- similar to mage, can be very good but also can be dog shit. it's pull can do actually decent damage from knockbacks. a lot of it's shit seems kind of overrated though, like perma charming one unit. ok. why the fuck not take something that could kill it or take charm on hunter? extra turn. ok. why the fuck not take cleric or druid? and a lot of it's shit is "all units in line of sight" which means unless you use a tp each turn to line it up, you fuck your team. want to like it but meh.
monk- monk's the biggest surprise to me in the game so far, i was expecting it to be kind of dog shit, but it's genuinely just kind of good at everything, and it gets bonuses for no items, so by design it doesn't need farming (the monk *not counted as armor* items can be good though), and generally a lot of it's rolls can be very adaptable so you don't feel locked into too much of shit. if you get bruise on basic attacks, even if your team fucking sucks, it can make it so EVENTUALLY the shit will be able to die. it can thorn stack, mark/magic weakness, free magic attack for 10+ each turn, do multi hits like fighter, ranged capability for far shit, built in tankiness. he walks around like that nigger. if you stack shit that does bruise, you can do 2+ bruise an attack so 4+ bruise a turn. almost never feels awful and very damn good, also has very good passives that can be inherited.
jester- is actually pretty interesting. it has no stat bonuses but most classes have like +3 and -2, so it's technically not THAT bad. copies all classes pools on level up, has a free reroll though, and also has some interesting unique abilities if you complete caves and boneyard, like a better metronome (random spell but weighted to be less shit) and it's not that hard to make synergies since everything's on the table. one of the most interesting things about them to me though, though it's not predictable, is their basic attack is semi randomized. which includes a cleric heal. that is very very interesting and can make them a cleric with much more variety/potential, but it's too random to count on or replace. they're honestly not that troll or shit or scary as they seem, but does require some luck. although, there is one thing i fucking HATE, HATE, about jester. i fucking HATE arthur, the jester miniboss that starts appearing. there have been 2 situations in mewgenics i've considered pretty genuine bullshit: arthur can use any spell. the area appears to affect the tiers, but in lab i've seen him cast "we are one" turn one. if you don't have a cleanse by like 3 fights, he has 85+ hp, and you just fuckin lose by default, especially when he waltzes around and drops inferno turn 2 and who knows what the fuck's up next.
second/third bullshit thing is in das future, the lightning boss disappearing every turn with a dot on it's very fucking annoying and retarded, and the tentacle arms hanging down that retract every hit is really fucking retarded. both of those feel like they're just going to be long and annoying for way too many builds unless you just explicitly have something at all times that can chunk HUGELY with minimal/no dots
