First, complete Sir Gavin's campaign to unlock Luna's campaign.
See here for my guide to chapters 1 and 2:Solution for Global Greening in CastleStorm IISolution for Essence of the Night in CastleStorm II
Chapter 3 starts in the Kingdom lands (green bits). You can teleport back to your underworld castles using the purple portals -- though you're unlikely to need to.
At the end of this chapter, you'll need to obtain
- 15 Snake Eyes (Witch's Tower level 3, Forest),
- 200 Metal Trash (Scrapyard level 1, Fields), and
- 25 Concentrated Screams (Spirit Drill level 2, Village).
This is on top of whatever you happen to hold at the time, but it's best to ensure you've build a Witch's Tower, Scrapyard, and Spirit Drill ahead of time, so you don't find yourself short of gold.
Try to keep your lands clear of enemies (so they don't tank your economy), but otherwise, the quickest path is to run straight for each objective:
1. Attack the castle you're standing next to
2. March East to the Tavern. Don't pay the gold : just fight the bouncers. Charge aggressively right at the start - you don't want to let their archers set up. Wave 2 is a solo paladin, so back up and destroy him with shotgun headshots.
3. Speak to the big guy outside the tavern, who sends you North-West to Hightower. Attack it for two waves of enemies. Keep right both waves to stop archers setting up.
4. Talk to the Empress, then return to the big guy outside the tavern. He'll send you South-East to the gate to the underworld. Run straight there -- you don't need to fight along the way. Talk to the grim reaper, then attack the camp a few squares to his north.
5. Backtrack North-West again
to Castle Neew. You can still just run past all the enemies -- just keep your own kingdom clear (you might need to tackle a zombie outside the fort you just captured). You're into another hero fight. Wave 2 this time is a griffin and
an archer. Run left so the griffin fires down to ground level and you can do massive damage with your power attack (only works if it's low). Take it down quickly before the archer arrives, then run back and pound him.
6. Talk to the blue butchers' tent for your next objective, WAAAAAAY South-East. Run to the Hidden Mansion where you started this chapter, and take the purple portal to Deadrealm Central for a short cut. Talk to the pumpkin horseman, then take a few steps East to the tavern.
7. Pay 50 gold, but no more. 500 doesn't make any difference, and 5,000 isn't worth collecting. March South, then East to the pumpkin horseman's capital, and attack. Objective completed, take the purple portal back to Kingdom Land, and talk to the big guy by the tavern.
8. Here's where you need an extra 15 Snake Eyes, 200 Metal Trash, and 25 Concentrated Screams. Build the relevant upgrades (see above); clear your lands of enemies; and end turn until you have them. Then, march North-West to build the stage for your finale.
After building the stage, speak to the pair next to Hightower, then walk East and speak to the Empress, which ends the chapter.