Coffins hide the roster
Some characters are not in the menu at first. They sit inside coffins placed on certain stages, waiting to be touched.
Find the coffin and walk into it. The character unlocks for every run after, not merely the one where you found it.
Plan the hunt
Each coffin lives on one stage. Learn which stage holds the one you want before you commit a run to finding it.
A coffin run is different from a clear run. You move toward the coffin instead of farming the center, so bring a build that survives on the move.
Do not force it early
Chasing a coffin with a weak build wastes the run. Get stronger first, then hunt with room to spare.
The stage selection page helps you pick the stage that holds your target.
Next: How to farm gold efficiently.