Seeing Double

Seeing Double is challenge #40. The goal is to defeat Mom's Heart. This challenge is unlocked by defeating Mother.

Difficulty

Otherwise a very standard run, the challenge comes from every enemy and boss placed naturally in rooms (as opposed to being spawned later) being doubled. Due to the high enemy density, damage may prove difficult to avoid in some rooms. It is recommended for oneself to be already familiar with the gameplay of Jacob and Esau prior to attempting this challenge.

Strategy

Room clearing items like Toxic Shock and items synergizing well with 20/20 such as Jacob's Ladder can be incredibly useful.
- Toxic Shock will only damage the original enemies in rooms, the doubled enemies that spawn will not take any damage.
As Esau begins the challenge with X-Ray Vision, Secret Rooms are instantly revealed, which may provide Jacob and Esau with helpful resources.
As Libraries are able to spawn in this challenge, they can be a valuable resource. The Bible can help with protecting one of the brothers as well as instantly killing both Mom and Mom's Heart, Book of Virtues will create helpful wisps in combination with other books (e.g. Book of Shadows), and Book of Revelations will help sustain either brother's health.
It may be wise to keep Silver Dollar if found, as the Shops it will spawn in Chapter 4 can be incredibly useful.
Eraser is an extremely powerful item for this challenge that can be found in Shops, as permanently erasing common enemies can help tremendously.
Mapping effects such as The Compass or The Mind can help quickly navigate through levels and avoid unnecessary risks.
Teleportation items such as 0 - The Fool, Teleport!, or Telepills can be used to quickly escape dangerous situations or skip rooms altogether. Glowing Hourglass may also be used to return to the previous room and revert any possible health loss.
Room clearing effects are particularly powerful in this challenge:
- The Necronomicon/XIII - Death will instantly clear more dangerous rooms.
- The Ace of Hearts and other Ace cards will instantly clear rooms with large amounts of monsters, producing numerous pickups in the process.
- II - The High Priestess can be an effective boss killer, greatly damaging or eliminating one or both bosses.
- Chaos Card, if thrown correctly, can instantly kill numerous troublesome bosses and enemies in a single throw.
Enemies and bosses in Challenge Rooms are not doubled, as they are not spawned when Jacob and Esau initially enters the room. This makes it worth considering to clear them for extra pickups and items.

Notes

Stonies, Death's Heads, and Mom are not doubled.
Encountering two Baby Plums and allowing both of them to leave will grant only one Plum Flute.
Prior to Version 1.7.5, Treasure Rooms did not appear.