Check the current unlock text
Essence is named in the supplied rebirth and progression material. Its exact source and effects should be read from the current in-game screen.
Spend for your next run
If an Essence purchase improves a reset loop, compare it against the rebuild route you will actually use. A benefit that fits your bottleneck is more valuable than a random upgrade.
Avoid fixed numbers without a version
No complete, verified Essence values are preserved in the supplied material, so this page avoids unsupported formulas.