Progression is what makes the next run start ahead. Spend unlocks where they compound.
What carries
Unlocks and upgrades persist between runs. Each run opens with more than the last, so progression is the long game under the waves.
Unlock the gap
Unlock the role your board lacks, not the flashy one. An unlock that fixes the first-wave gap compounds through every later wave more than a late toy.
Deepen the pair
After the gap, unlock the merge that deepens your core pair. A run that opens covered and scaled clears further than one that opens strong but thin.
The path
Start with the first-wave need, then the pair, then the spike. Progression spent in that order makes every run start stronger than the one before.
The best builds guide shows the board the unlocks should serve. Unlock toward that.
Spend meta currency on the board you play
Progression unlocks (new bonkers, starting gold, perks) carry between runs. Unlock the bonkers the best builds guide uses first, then the economy perks that fund merges. Scattered unlocks that do not fit your board waste progression currency you cannot get back quickly. Starting gold upgrades let you merge one wave earlier, which compounds across the run.
What carries into endless
Everything meta carries, so a focused progression tree makes the next endless start stronger. The endless guide covers the board shape that benefits most; unlock toward that shape, not toward a unit you never field.