Steven

Steven is a boss that can appear in: Each Steven has 140 HP.
 * Only in.
 * and the.

Behavior
Phase 1
 * Big Steven chases Isaac and periodically charges increasing its speed, but stopping to catch his breath afterwards.
 * Steven Baby shoots a projectile towards Isaac if not behind an obstacle.

Phase 2 If Big Steven reaches 50% HP, they separate: Small Steven can be targeted and killed first with no change to either Steven's behavior.
 * Big Steven continues the same patterns.
 * Steven Baby begins charging furiously at Isaac.
 * Both, when killed shoot out projectiles in all directions.
 * 8 projectiles each.
 * Big Steven: Two rows of 8 slow-moving projectiles that travel over obstacles and off-screen. Small Steven: unchanged.

Trivia

 * Steven appeared in the original Binding of Isaac.
 * He is a rare alternative to Gemini.
 * Steven originated from the 2009 flash game Time Fcuk, which was created by Edmund McMillen.
 * Steven can appear in Greed Mode prior to his prerequisites being completed.
 * As they appear in Time Fcuk and on the boss art, Big Steven and Steven Baby have the back of their heads attached. However, their attachment does not appear this way in-game. This is likely due to Big and Small Steven having the same function of how Contusion and Suture are conjoined, only without the long cord holding them together.
 * According to Edmund McMillen, Steven is connected to Isaac.
 * Steven also appears in The End is Nigh, another game created by Edmund McMillen.
 * One of the images that can appear before the start of a new run states: "GET IN THE BOX", which is Steven's unofficial catchphrase from Time Fcuk.
 * It is also likely an allusion to both Time Fcuk and The Binding Of Isaac taking place inside some form of box.
 * Big Steven's appearance as one of Delirium's forms shares the appearance of Ash, the main protagonist of The End is Nigh.
 * Steven Baby's projectiles have a completely unique visual design while Big Steven's death projectiles have both unique visuals and behaviour.
 * These new designs are made to coincide with Edmund's project Øuroboros, which also features Steven; teased in 2016.
 * In the Bestiary, Little Steven is referred to as "Steven Baby".