Blue Bomber is Challenge #23 introduced in Afterbirth. The challenge is started as ??? with Kamikaze!, Pyromaniac, Mr. Mega, and Brother Bobby. No treasure rooms. The goal is to defeat Satan.
??? is blindfolded and cannot fire tears. Players will have to use Kamikaze! and bombs in order to defeat enemies, with Brother Bobby generally as a last resort. Because Pyromaniac prevents damage from being taken from explosions, players can use Kamikaze! whenever they please. Using it as an offensive weapon can be very dangerous, as the player will have to closely approach enemies, increasing the chance of taking damage.
As ???, health is crucial due to the absence and inability to obtain red heart containers. Any form of damage is threatening, as hearts may be hard to replenish.
- Finding an item which revives you as another character, like Lazarus' Rags or Judas' Shadow will make the run trivial: After reviving you will be able to gain red heart containers, therefore healing yourself infinitely as long as you have them, effectively making yourself invulnerable. Clicker will also work, though the odds of getting it are small.
- With Kamikaze!, rooms can be skipped without having to clear them. This can especially be useful against larger and more challenging rooms.
- Broken Remote allows for essentially infinitely reusable teleportation, enabling entire floors to be skipped, except for boss fights.
- The player should use bombs for boss fights or harder enemies. Due to Mr. Mega, not only do bombs deal increased damage, they also have a far larger blast radius.
- By dropping a bomb then using Kamikaze! to propel the bomb towards enemies, ??? can safely deal damage from afar with relative ease.
- Kamikaze! effectively gives ??? infinite explosives, so it’s a good idea to blow up rocks to look for Crawl Spaces, and ??? can search for Secret Rooms at no cost. Also, the player can blow up Tinted Rocks, skulls, and blue/purple fireplaces, which may contain Soul/Black hearts. However, be careful about blowing up skulls before you’ve cleared a room, because they may contain Hosts.
- Be careful about bombing objects that could deal damage to ??? upon destruction. It's risky to use Kamikaze! around Mushrooms since they may release damaging gas or around Polyps as they may explode into bullets. It may behoove the player to destroy these obstacles via bombs to prevent such scenario from occurring.
- The player should not replace/reroll Kamikaze! as without it the challenge will be extremely difficult or even impossible. They should be very careful around Dice Rooms, Missing No., and certain dice items.
- Familiars and BFFS! are useful in this challenge, since it allows you to deal with enemies that are dangerous up close more easily.
- BBF and Bob's Brain are especially useful as they gain increased damage from Mr. Mega, while Pyromaniac will protect ??? if they explode close by.
- The Polaroid is preferred over The Negative since the shield will trigger every time ??? takes damage, allowing you to get up close to spam Kamikaze! safely for a brief moment.
- When fighting Mom, a reliable strategy is to stand in the corner and defend yourself. Whenever she exposes herself from nearby doors, go to them and use Kamikaze! from the side. You cannot be hurt by her (and Satan's) stomping attack (see Pyromaniac), but watch out for its knockback.
- Due to the immunity to Mom' stomping attack, Mom's Toenail has improved usefulness.
- Items that modify bombs, such as Bomber Boy, Bob's Curse, and Butt Bombs are especially useful, as they provide a greater range for the detonation, a poison effect, and damage to the entire room, respectively.
- Glitter Bombs provide an unlimited source of pickups, including soul hearts.
- If the player can somehow switch to characters that have red hearts through items like Lazarus' Rags, Judas' Shadow, or Clicker, getting 2 or more red heart containers will grant the player infinite healing from Pyromaniac and Kamikaze!.
- Gaining flight allows ??? to quickly navigate rooms, to avoid having to use Brother Bobby to reach faraway enemies, and to better maneuver around for Kamikaze! usage.
- Transcendence, which grants flight, can be found in Secret Rooms.
- Trinity Shield, which is incredibly useful for blocking shots, can be found in Angel Rooms. Since ??? can't fire tears, you can focus on defending yourself from enemy projectiles. This is especially useful in the battles with Mom's Heart/It Lives and Satan.
- Sleeping in a Bed will give you 3 Soul Hearts.
- Since ??? is unable to use Red Heart pick ups, Dark Bum is extraordinarily useful as he gathers the hearts and converts them into Soul Hearts and Black Hearts, as well as the occasional friendly blue spider.
- Camo Undies are especially useful. Every room you enter will have confused enemies and with Kamikaze! they will not attack ??? as long as you do not use the fire button for Brother Bobby or other familiars.
- Acquiring Chaos makes this challenge far easier. Allowing bomb-related items such as Butt Bombs and Sad Bombs to spawn in shops, Devil/Angel rooms and as Boss rewards, these items allow Isaac to hit enemies passively from afar, or use an unlimited Tammy's Head-style effect, especially powerful when combined with Brimstone.
- If you happen to skip Satan (using I AM ERROR or Sacrifice Room's 12th activation) the golden door will not appear in the Dark Room and upon killing The Lamb you will still get the completion trophy.
- Converter does not convert soul hearts into red heart containers; it just takes 2 soul hearts and gives nothing in return.
Note that Gold Bombs have fixed appearances in certain room layouts even before this achievement is unlocked. The achievement simply allows them to spawn in place of other bombs, like Golden Keys.
- The title for this challenge is a possible reference to Mega Man, as he is commonly known as the Blue Bomber.