The Pure Land (Merciless)

獄楽浄土 超極ムズ is an Advent Stage unlocked after clearing River Acheron. It consists of a boss fight against 491. When clearing this stage, you have a chance to unlock 522-1.

Battleground

 * 491 spawns as the boss after a few seconds. Soon after, Doge Dark starts spawning at a slow rate.
 * After 26.7 seconds, Gory Black spawns every 58.7~60 seconds, up to 5 can be seen in total.
 * 3 Ginger Snaches spawn after 26.7 seconds, with 3 more spawning after 146.7 seconds.
 * 3 Doge Darks spawn after 86.7 seconds, with 3 more spawning after 193.3 seconds.
 * 5 Ginger Snaches spawn after 253.3 seconds.

Trivia

 * This is the only Advent Stage without a No Continues restriction.

Reference

 * https://battlecats-db.com/stage/s01217.html