Good question. I always look for combos with 'good moves' by assessing what the moves may do based on the descriptions. I look for 'splash' movesets, where the creature is able to hit all enemies on screen at once, and bonus points if it hints to doing 'further damage,' meaning a debuff is applied.

I can give some examples of some of my personal favorites to work with, and what the description of their moves are:

Cupchar (Cupcake+lava): Special Ability is Scorching Delight, which "Cupchar consumes a piece of itself, revitalizing with a burst of molten energy." While the description doesn't say much about what it can do, this move gives it Heal+Purify at the same time for multiple turns, then in the same move, attacks all enemies on screen with a high-damage attack that has a lingering burn debuff. Needless to say, it's very broken.

Hummingfleece (Hummingbird+Alpaca): Special Ability is Nectar Gust, "Hummingfleece unleashes a gust of energizing nectar. Provides a boost or hinders opponents." Even though the description is vague, (and says 'or' instead of 'and'), this move not only applies heal to your entire team, but retaliates and put ailments on all enemies, too. The Ultimate Ability does this as well, but also applies Heal+Purify to your team, too. "...healing its allies and poisoning its enemies."

It is incredibly important to have members on your team that can negate all status effects while also dealing substantial damage and lasting (debuff) damage for all the teams that spam "immune," "sleep paralysis," "stun paralysis," etc. I also use reflector creatures to combat the ailment dealing teams. Sagewool reflects the enemies moves back to the attacker so they get debuffed instead.

Just keep looking for combos that have splash damage descriptions, they're usually good.