What I mean is, make abilities where people can put certain abilities together into a single multi-effect massive cost ability.
Like Flare+Webs.
They need to be the same type of ability, such as both ground cast or both self cast.
Though, they probably need to be the same cost type to do it...
Though it'd be fun to have cross-cost abilities as well.
Magelight+Hunter. Stam+Mag Cost. Both a fighters and a Mages.
Function: one animation, uses range of the lowest possible range, each effect's radius is based off the ability it's from, and duration likewise.
Cost = cost of A + cost of B. Counts as both abilities slotted. If the cost reduction is limited, then only the cost of that portion is reduced and the rest is still normal.
Such as Magelight cost would be reduced by Mages Guild passives, reducing the Mag cost, and Hunter reduced by Fighters Guild, reducing stam cost, but Mage's doesn't reduce the stam cost and Fighter's doesn't reduce the mag cost, because those portions are the other guild ability.
Hope I explained that well enough.
Abilities must be very similar in order to be unified this way, and in some cases they may naturally be reduced on cost because they both apply the same effect for the same duration, just have different side effects or slotted bonusses.
Though flare is a revealing ability, it cannot be merged with Magelight or Hunter because it is a ground ability and they are self abilities. However, Flare can be used with snares like Webs and Caltrops, roughly doubling the cost though.
I don't really see this as being unbalanced other than it allows more slottings essentially and cutting out of about a half second of cast time in most cases. Good for people who want to one-bar anyways.