When you have multiple skills or items that you use regularly, it can to be a hassle to left click the skill then right click wherever to actually use it then left click another skill to swap back to it. It would be more convenient (and I'd imagine easy enough to code) for non-targeted skills (self-buffs etc.) to be instantly activated via right click in the same manner that consumable items are now. A further suggestion is for targeted items and skills to also be usable while 'in hand' without changing the currently active skill/item. For example, the player left clicks their single powerful bolt -> it appears in his cursor -> the player right clicks an enemy -> the bolt is fired and is consumed as normal -> the player can immediately return to right clicking their active attack spell. Or for skills: the player right clicks their teleport skill -> the sprite of their spell appears in their cursor -> the player right clicks an empty tile -> the player is teleported, cursor is cleared, and they may immediately resuming firing off their active bolts. That latter part might be too confusing for newbies to the interface, I guess, but all the extra clicks to active a passive buff feels unintuitive as it is now.
I know you might not have access to equipment with this particular feature, but you can use your mouse wheel to switch between what is selected.
There are also shortcuts for spells: 1 for skill in the first slot, 2 for the second etc. Also, we have multiple skillbars now, there isn't a necessity of left clicking everytime.
