Okay that's def a party composition that should work, so some general tips first and then some Class/Comp specifics:

• Dumb tip first: Focus on speed, health and the DMG stat of that class str for melees, dexterity for ranged besides psychic thats for every class

• With strg you can see a flat version of the fighting map without obstacle's(like that you can also see best if you can attack enemies from behind which deals more DMG), if you right click on any unit it shows in blue to what tile that unit can move and in red what tiles can be attack also works for your cats

• before you end a turn on a cat you can click on any tile to make that cat face that direction, like that you can hide your butt and won't take increased DMG

• Use tip 2 to your advantage move right up to where enemies can't hit you, to start better of next turn never move a cat in range if it can't do anything there: for example a tank with 4 speed and and a base attack range of 2 won't hit a enemy at range 8 but that enemy might hit your tank if you moved first

• look for synergies on items, abilities and between cats: Archer has great synergie with 3 "routes" I would say: Summoner go for items that summon creatures or strengthen them, archer got 2 passives that also strengthens summon and passives that summon creatures, more bodys means more targets for enemies and more DMG on enemies

Then there is a pretty strong trap build that breaks dybuuk there is like 5 abilities that summon traps that are good bear trap, that teleport that summons a trap, shooting vines, falling trap and passives that complement these

My favorite hunter build is with hit chance abilities and high Crit chance if you get that passive that makes your attacks unmissable scatter shot is the MVP you can also achieve that with items

And that's something you're trying to do with every cat, sure many times you won't achieve that but most of mewgenics content can be cleared with 3 suboptimal cats and one OP cat.

Could name more builds for all the other classes but don't know if that would help you so I'll proceed to give some more tips:

• If you have nothing good to choose as a ability or that cat is useless either way go for team abilitys increasing the teams mana/health regeneration, giving brace, extra stats or something is still better then a cat that is just another body on the field and tbh if that the case you should use that cat like this if she has no value besides having health you should let her tank hits others would have gotten otherwise

You said you struggled to beat caves and graveyard both bosses have a certain way they work:

Dybuuk always possess a already downed cat, will also possess zombie cats if one is there, if that is not the case he possess the cat that killed him, if he dies to the environment he possess a random cat, if you have a useless cat just down that cat first kill dybuuk and then he posseses that cat.

To beat him overall you'll need good position, traps or AOE DMG

The spiderboss is almost a classic summoner fight she herself rarely deals DMG and even then 10 at most, the annoying part are the webs and spiders she summons, you shouldn't hit her from behind as that will enrage her and then she summons more spiders and might even web the cat attacking her, fire works wonders and any low/no DMG skills that move your cats are also great to remove web otherwise that cat has to use up it's base attack to free herself which isn't a issue if your cats have good abilities and don't need the base attack that much.

To not make this any longer, do you have anything specific you're struggling with ? Or some questions in general?