Well, geo produces oil and poison which can both be set alight by fire. So geo/pyro is usually a good combination. (1) and (2)
Hydro produces water/ice which cancels out -- and gets cancelled out by -- fire effects most of the time. So hydro/pyro is generally a bad combination. (1)
Note also that a large portion of the hydro arsenal can be used by characters without notable investments into int, i.e. the healing spells. I'd actually recommend to dump those on a non-int character (I use my warrior(tank)) to 'save space'.
Now hydro would combo pretty well with aero, since the two together produce shock/stuns. There's no significant combo potential afaik between hydro and geo... except maybe larger poison puddles?
I also feel like mentioning two things which would go against dropping geo, at least against dropping it entirely:
1. Geo has quite a few of the (rare) spells that check against physical armor. That means they support parties well that focus on physical damage/cc.
2. Geo also has poison skills in it. If you have undead in your party (Fane or custom character(s)), then those spells will play an important role in keeping them alive.
(1) 'Usually' because there may be situations where synergies/combos may not be wanted, e.g. mobs with low poison, but high fire resistance, or mobs with low hydro, but high aero resistance. At some point you might want fire clouds, in which case water + fire is a required combo, but... that's rare and you can always replicate such effects by using disposables (e.g. arrows, water bombs, grenades etc.).
(2) As a famous mage once said, 'As the size of an explosion increases, the number of situations it is incapable of solving approaches zero.'
Last edited by Terodil; 25/09/17 12:32 AM.