The Corrupt Heart is the final boss, fought in Act 4. It is very powerful; its innate powers and buffs it gains throughout the fight can prove very difficult to counter. Because of its Invincible buff, it can only take 300 (200) damage per turn, rendering strategies that rely on heavy damage less effective. Additionally, it will gain incredible amounts of Strength on its fourth buff and onward, so killing it quickly is also important.
Always starts with Debilitate. Uses Buff every 3 turns starting from turn 4.
Otherwise, has a 50% chance of using Blood Shots followed by Echo and a 50% chance of using Echo followed by Blood Shots.
Do not use either of the first two cards in this list on a turn where The Heart buffs. It will clear the strength down debuff, then gain back the strength you made it lose from the card, essentially making you give The Heart free strength.
Any source of Weak will also be extremely valuable against both of The Heart's attacks.
Sources of damage negation such as Intangible and Buffer can be very effective against the Echo attack. Intangible is also reasonably useful against Blood Shots, as it will always lower the damage to 12 (15), whereas Buffer would only negate 1 (2) of the attacks.
Any effect that triggers on-damage or on-attack is very good against The Heart due to it triggering 12 (15) times for each Blood Shots that The Heart does. This includes:
Medical Kit can be useful against The Heart, as it will allow you to remove the many statuses it will inflict on you, but beware of its Beat of Death power, as it will trigger whenever you play any card, including curses and statuses.
Tungsten Rod and After Image can completely negate Beat of Death 1. Both of these, or 2 copies of After Image, are necessary to negate Beat of Death 2, applied on The Heart's second Buff action.
Patch V2.0: The Watcher
Slime and Heart enemy SFX no longer play when game is backgrounded.
Patch V1.1: The Dealer
Fixed Invincible power with interactions such as The Boot and Block.
Weekly Patch 55: Blur
Adding VFX for the Heart's buff move.
Adding VFX for Heart's debuff move.
Weekly Patch 53: Blizzard
Beat of Death Power now damages you after a card's actions completely resolve.
Invincible Power tooltip now correctly matches the icon and shows the correct amount.