Hearts of Darkness (Merciless)

Hearts of Darkness (Merciless) is a secret stage in Growing Strange. It can be accessed randomly after completing An Elder Secret (Merciless). Completing this stage yields an Elder Catfruit Seed, with a very small chance of an Elder Catfruit.

Battleground

 * At the beginning, a Dark Otter and a Tackey will spawn. Nothing else will spawn until you hit the enemy base.
 * When the base reaches 99%, the base will spawn up to 2 Doge Darks, 3 Tackeys, 11 S.B.Ks, 5 Dark Otters and 1 Razorback. Once they are killed, nothing else will spawn.

Reference

 * https://battlecats-db.com/stage/s01162-01ex03.html