Bosses are the marks between stretches of waves. Each tests the board you built.
The shape
A boss is tougher than the waves before it and walks a lane. The mistake is treating it like a big wave when it needs a covered lane and a spike.
What it asks
Each boss hits harder and often targets the thin lane. The wall is the lane you skipped, not the boss’s size. Deepen the weak lane before the mark.
Preparation
Cover every lane, then merge one unit into a spike for the boss. Hold gold for a last buy if the shop offers the role the boss exposes. A covered board clears.
The clear
A board that covers all lanes and has one merged spike is what beats a boss. A board of heroes with a hole loses to the lane the boss takes.
The wave guide shows where the spike sits, so you can build before the boss mark.
Boss waves are scheduled
The boss (spike) appears on a known wave, not at random. Bank gold in the waves before it and drop your strongest merged unit on the lane it targets. Bosses hit harder and often have a gimmick (shield, rush), so a pure-dps lane without a tank will fold. Pre-place a tank there even if it means a thinner other lane for one wave.
Build to the mark
Know the spike wave number from the wave guide, then stop buying filler two waves before it. Spend that gold on the merged unit that meets the boss lane. A boss you meet under-built is a reset; a boss you pre-built for is a clear.