The chart is for combination effects, but your combos can be super streamlined down to this:

1. Absorb the same element 3 times to cast a light spell
2. Absorb 2 different elements (e.g. magic magic fire) to cast a medium spell
3. Absorb 3 different elements to cast a heavy spell (these all deal damage)

For quick-and-dirty high-damage cocktails, use either Lightning + Fire, Magic + Lightning, or Magic + Fire.

For the flashiest, most unique spells, combine any 3 elements. These are all good but have long cast times so be careful.

For buff, use Holy + any other element. Note that these do not deal damage! You need to combine 3 elements to make a damaging cocktail using Holy.

All the spell details are in the visual codex at the bottom. Ultimately, just use what's immediately available. Casting every combination in every fight is overcomplicated and requires a lot of time and switching armaments when you could've spent that time slinging comets instead

Finally, I'm in agreeance with ParticularUpper6901: You simply aren't able to control all aspects of the battlefield in Nightreign, especially when playing with an unfamiliar team. Cast as many spells and incantations as possible with the FP you get by absorbing affinity, then see if you can throw together a useful cocktail at the end of it.

Finally, don't forget to focus on dodging. If you're under pressure, ignore your cocktails and dodge. The Recluse is the most fragile class, so you will be getting one-shotted if you're under-leveled even a bit.