Which champions would be powerful in this Invasion mode other than the ones which have SG skins?

If it was possible to use them, of course.

I think would be really powerful. His E could be useful against the voidlings, his windwall could counter the Vel'Koz beam spam, and he could rush a Phantom Dancer with that 2600 gold, or a Statikk to clear the Voidlings faster.

would also be very powerful, his sustain would be so valuable in this game mode where you need all survivability you can get, and with his pool he could counter Rek'Sai and the giant Vel'Koz's beams. Plus he is very tanky.

And considering that the Vel'Koz's are basically champions (Jinx can get resets off them) would also be powerful on this game mode with his ult. Reseting off the Vel'Koz, he could kill all them very easily, and dodge the beams with his Alpha Strike. He also synergizes well with Ardent Censer.