Slumbering Essence

Enchantment

If this card is in your hand at the end of turn, reduce its cost by 1 until it is played.

Held at end of turn: if the enchanted card is still in your hand when your turn ends, its cost drops by 1, and the reduction lasts until the card is played.
Grows by turn: the check runs just before the end-of-turn discard, so a card kept through Retain, or through an effect that retains your hand, gets cheaper every turn it is held. A 3-cost card held for three turns is free.
Once played: the discounts vanish and the card returns to full price.
Eligible: any Attack, Skill or Power.
Unreachable: nothing in this build grants it, no relic, event or card creates Slumbering Essence, so it is defined in the data but unreachable in a run.

Comes from

Nothing in this buildNo relic, event, potion or card grants it yet

Worth knowing

Best cards to enchant

Retain cards are the natural home, since they stay in hand and the discount accumulates. Reap is a 3-cost Retain attack that becomes free after three held turns. Reaper Form is a 3-cost Retain Power that does the same. Snakebite costs 0 after two turns. Sow is free after one. Well-Laid Plans retains a card each turn, which lets a non-Retain card such as Bury slumber too.