Gnomeregan is (as of writing) the newest dungeon added to Warcraft Rumble and by far the strangest one. Where the other dungeons lend themselves towards straightforward slugfests, Gnomeregan has unusual mechanics to contend with. It's a medium-difficulty dungeon compared to the current set, with most of the difficulty being found in the firepower brought by the second boss, Electrocutioneer 6000.
Crowd Pummeler
A very strange boss, this mechanical menace revolves around revolving! The three main mechanics found in this map are the wandering target, the two protection belts, and the knockback from the boss.
The first is similar to the Dreadnaught map in Westfall. A target roams the map in a rectangle pattern in the top half of the map. When it catches an enemy mini (yours), the boss fires a missile which deals moderate damage and knocks back all minis caught in the radius. Any non-flying mini knocked out of bounds dies instantly, so this can be devastating to slow, expensive minis.
The second mechanic are the two protection belts located directly north of your base and south of the boss.
A mini wearing one will become temporarily immune to damage and also the knockback effects from the boss and the missiles. Leaving it untouched causes a Safe Pilot to be dropped in and take it instead. This isn't devastating, but a little bit annoying, so try to avoid letting them stay up long enough for that to happen.
Finally, the last mechanic involves the boss itself. When attacking, the Pummeler spins around, hitting all nearby targets and knocking them back, same as the missile attack. This can be pretty annoying, as it makes melee minis almost unable to hit him. Ranged minis can avoid the knockback, but the tanks needed to protect them are swiftly killed, so the Pummeler is pretty hard to assault overall.
Key features of the map:
Two chests, one straight up to the north from your base, the other near the meeting stone. These are points you'll want to be taking anyway, so you'll naturally gain the extra gold as you control the map. There's also two mines near the meeting stone. You'll want to deploy your kobold up and slightly to the right if you want the miner the path towards both, otherwise, he will just continue towards the boss.
So, how do we crack this mechanical coconut? First, securing the middle meeting stone is of paramount importance. It provides access to a chest, two mines, and the right protection belt. Of the two belts, the right one is more important as when wearing the left, most minis cannot reach the boss before the effect wears off.
Attacking the boss is tricky because of the knockback. A flying tank like Gargoyle can help, since it survives the knockback and allows ranged minis to keep swinging. As we'll see this does come at the cost of a useful mini in fight three, where flying minis are fairly ineffective. Alternatives are just burning the boss down with Safe Pilots, Whelp Eggs with Flame Burst, or Execute, all of which deal moderate damage. Sneaking in a Defias Bandit to stun and create an opening for other minis is another.
Otherwise, you can exploit the fact that the missile is launched from the boss. That means when a mini steps into the target, the boss stops swinging at targets next to it. Strategically timing a push so a mini on the left is wearing an invulnerable belt (and therefore survives the missiles) can create an opening for your push, as the boss vainly tries again and again to launch, rather than fight your army.
Electrocutioner 6000
The most straightforward yet difficult boss of the three. The Electrocutioner sees the return of Rocket Towers, placed on either side of a bridge connecting the base to the boss. Protecting the towers are clouds of poison, which chip down any assaulting minis. Finally, the boss periodically spawns 3 leper gnomes, one heading down each lane.
Resources come in the form of a chest on the bridge and a mine on the bottom left and top right, near the towers and clouds of poison. Without control of the towers, these are more-or-less unobtainable for the player, so securing the Rocket Towers is the crucial step to conquering the mission.
It's important to note that the poison continues to damage your minis even after you take the towers. This makes them less attractive as deployment locations and much harder to defend, though you can deploy just on the edge and avoid the poison when preparing to assault the boss.
The strategy for Electrocutioner is fairly simple. You need to take the towers and hold them as quickly as possible, because otherwise you are at an insurmountable resource disadvantage. The left tower is slightly preferred because of the mine closest to you, though note that the right tower would allow you to deny both mines to the boss.
As for taking the towers, the poison cloud pops Whelp Eggs immediately, so that can be a solid option. Execute is also good against the high health towers. Otherwise, the poison and rocket attacks necessitate sending in your beefiest minis to endure. The bridge does allow the boss to defend the tower using ranged minis, but a well-placed Safe Pilot will clear that up.
Once you've taken the towers, attacking the boss isn't particularly complicated. It has a fairly powerful beam with a ramp up time and a Chain Lightning attack, so mini positioning is important, but you're on the home stretch at that point.
Mekgineer Thermaplugg
The final boss of Gnomeregan is actually the easiest. Unlike every other boss in the game, defeating him doesn't involve attacking him directly. In fact, between the damage shield and his overwhelming firepower, a direct assault on the maniacal Mekgineer is nearly impossible.
Instead, the fight revolves around popping these blue zappy lightbulb things on either side.
When you get the last hit on one, a bomb spawns on the conveyor belt and damages the boss. When the enemy does, one bombards your base instead. The fight therefore revolves around controlling the left and right lanes and reacting to bulb spawns. You have to be careful not to overcommit, as any minis that make it past his army are just annihilated by Thermaplugg.
You have a very large resource advantage on this map. Two gold mines are directly in front of the base for easy access. If you take the Auctioneer's Contract relic (Each Gold you mine partially Heals your Towers and Base), the fight becomes incredibly easy. The only real threat you face is losing control of the bulbs, but the easy flow of gold nearby will heal all that back up.
Flying and siege minis cannot attack the bulbs. This makes siege minis more-or-less useless, and flying minis only useful for contesting the sides surrounding the bulb spawn areas. As a flying, siege mini, if you brought Gargoyle for fight one, you should never play them here. But if you've brought Safe Pilot, she can snipe two bulbs at once if you place the target carefully in the middle.
Overall, a fairly easy fight. You play counters what the Mekgineer deploys and try to keep some gold in the pool in order to deploy minis to take bulbs. If you've made it to this point, the dungeon reward is yours.