Hey, everyone! I'm a little late to the party, but I think I've got a solid idea that'll be fun to work on even if I don't quite meet the deadline. Since I'm hard-pressed for time, and the details are worked out pretty well in my head (knock on wood), I'm not going to do a full-fledged concept sketch, but rather a brief breakdown of what I intend to include in my scene so I can get started faster.
The Altar of Storms is a significant monument in Warcraft lore, being used by Gul'dan in the Second War to channel fel energy into ogre magi, bestowing them with power and intellect. Many Altars were later repurposed to aid in reviving fallen heroes of the Horde during the Third War. There are only three remaining Altars in the world of Azeroth, but a few similar Altars can be found in use by the Burning Legion in Outland, as seen in my moodboard below.
I've always loved Blackrock Mountain, and though the invasion event isn't taking place in the Burning Steppes, it seemed like an excellent place to set up a combat scenario between the Horde and the Burning Legion. I'm not sure how many characters I'll be able to put in the scene with such limited time before the contest ends, but ideally I'll have some Goblin, Troll, and/or Orc craftsmen retooling the Altar of Storms, a primary defensive position at the bridge where some heroes can fend off the approaching Infernals, a Horde staging area with first aid tents and supplies, a few catapult emplacements, and some sort of demon leading the invasion - maybe a Nathrezim or a Doomguard.