Merging is how a board grows past the early waves. Done wrong, it opens a lane.
What a merge gives
Two same units become one higher tier. The result hits harder and often reaches further. That scaling is what clears late waves a tier-one board cannot.
Merge on coverage
Only merge when every lane is still covered after. A merge that trades a unit for a spike leaves a hole, and a hole ends the run. Coverage first, then deepen.
Hold the copy
If the second copy is the only thing on a lane the next wave needs, hold it. The merged spike is worthless if the lane behind it is open.
Stack the synergy
Merge into a unit that already fits your synergy. A higher tier of the wrong role is still the wrong role. Grow what the board wants, not what the shop offers.
The synergy guide covers which roles combine. Merge into the pair that multiplies.
Merge before you buy
Two identical bonkers on the board should merge the instant you have both — a merged unit has more stats than the two apart and frees a slot. Hold one copy only when you are saving for a specific higher merge the synergy guide names. Merging also resets the unit’s position cost, so a merged tank up front is cheaper to keep alive than two separate ones.
Merge into the pair that multiplies
Not every pair is equal. The synergy guide shows which roles combine for a bonus; merge those pairs first so the unit you build actually multiplies the lane. A random merge is still better than none, but a synergy merge is what clears the spike.