So I went around and bought little source books that I could find here and there and pieced together 7 of the combinations:
Source hydro + warfare = mass cleanse wounds
source fire + scoundrel = mass sabotage
source aero + huntsman = Evasive Aura (like the aero skill evasion, but 90% instead of 100% and 1m instead of 20% movement. Notably worse, and doesn't mention actually increasing your allies' evasion and movement. Due to being called aura and costing 2 ap and a source, I'm going to assume it will actually work as an aura.)
source necro + hydro = Blood Storm (4 AP 3 source, sets disease and decaying touch on enemies. No mention of damage, but the very high source cost might suggest otherwise?)
source huntsman + hydro = Mass Cyrotherapy
source scoundrel + geo = venomous aura (as venom coat, but an aura around caster and lasts 4 turns)
source warfare + fire = master of sparks (target character and surrounding allies recieve sparkmaster status which adds a chance of fiery sparks to melee attacks, I'm assuming this means it's a mass "sparking swings" book)
So it basically seems like most of the source skills are a mass version, with exceptions.
