Can the opponent make use of it too?
The opponent can't use your creatures, so no.
1) How exactly would this work with creatures with click-to-activate active abilities? Would you have to discharge them before using their ability (or vice versa)? Or something different?
Currently I'm thinking that, because it takes a lot to channel this energy.
2) If the closest enemy creature is Immaterial/Burrowed then would the discharge's target change to the next closest creature?
Yep :>
The order is the one they're played in and sit on the field.
I'd be interested to see what this would look like in game. Any visions on what kind of graphic effects it would have if implemented?
Indeed, the visual effect was what gave me the idea. The concept of a massive wave of Aetherial energy pulsing through your forces and unleashing on your foes is quite impressive. The wave originates from the right side of the screen and gathers in your creatures as it passes by, making them glow turquoise, possibly shift slowly between turquoise and white, sort of like the visual effect of Super Knuckles in Sonic & Knuckles (except he glows pink). This casting animation is accompanied by a pulsing electric sound.
When you discharge, electric sparks crackle between all creatures on the field, and pulses launch over the screen simultaneously with a brutal, crackling noise. This is, in my head, one hell of a light show.
I couldn't have asked for a better topic in which to post a 4000th time :>
<3
There will be moooooreeee~