Big Dog

Big Dog is the second boss of the game, located in the Scrapyards. It initially lays dormant, but will be awoken if one of several conditions are met
 * The Player gets too close
 * The Player maintains line of sight for a total of 5 seconds (150 frames)
 * The Player deals 30 or more damage to it while it is asleep
 * There are fewer than 3 enemies left on the level

Phases

 * Big Dog has three behavior phases and will cycle between them in random order. It also explodes upon death, covering a wide area. Be careful where you stand when it dies!

Walk Phase
 * Big Dog moves in the direction of the player, but doesn't deal contact damage.

Spin Phase
 * Big Dog spins very quickly, and 6 lines of slow moving red projectiles spiral out of its body. The projectile pattern will have randomly placed gaps.
 * Upon waking, Big Dog will always start with this phase



Missile Phase
 * Big Dog shoots volleys of 3 homing Big Dog Missiles around him.

Big Dog Missile

 * Will target the player and slowly move towards them.
 * They deal 5 contact damage.
 * They bounce off of any solid objects or walls and take damage whenever they do so.
 * When hit, they will turn around and be pushed back.
 * After taking enough damage, they will explode. The explosion deals 5-10 damage to everything that's near, including Big Dog itself.
 * They don't drop rads, but have a higher chance to drop ammo and health pickups.
 * A portal won't open if one of them is left floating in the level.
 * They don't count towards your kill count.
 * Attracted by Eyes' active ability.

 Loop Version Looping the game causes Big Dog Missiles to constantly fire red projectiles. Each projectile deals 3 damage. Big Dog will fire an additional missile each loop. Missiles will shoot out projectiles faster with each loop.

While spinning Big Dog will fire two additional lines of projectiles each loop.

Big Dog's health increases by 80% with each loop, which is more than for other bosses.

Trivia

 * Big Dog is a machine built by humans, which originally wasn't suited for combat and destruction. Currently, he will attack whoever disturbs his sleep.
 * Big Dog's design was inspired by Cerberus, a three-headed dog that guards the gates to the Underworld in Greek Mythology.
 * Big Dog is the only enemy in the game that splits into several parts when killed.
 * Big Dog was added as a playable character on 1st of April 2015, as an April Fools joke, and removed a week after in update #67.
 * Big Dog Missiles used to be a gray colored, static sprite which made them difficult to see in the heat of battle. That was changed in update #72 and they got animated in update #81.
 * Big Dog's boss theme is "Dogs".