Its primary attack involves it bursting out of the ground and diving at Isaac's position, dealing normal touch damage before burrowing back into the ground at that spot. Just before it re-enters the ground, 4 blood projectiles fire out in an X pattern from the last segment of its body. In its secondary attack, Pin's head pokes out of the soil and it launches an explosive, IPECAC-like shot toward the player's location.
It is best to shoot directly towards Pin while it is diving at Isaac as this will cause the most shots to hit the target.
Pin will generally dive out near where it last landed, but it may actually burst out in an entirely different spot in the room.
After it pokes its head out and uses its explosive shot, Pin will emerge from the same hole it poked out of before. Pin still takes damage despite being underground after this shot, so maintain fire on where he drops back under ground.
Sticking to the walls and moving slightly everytime Pin jumps makes it near impossible for Pin to hit Isaac.
It generally dives exactly where Isaac are with no regard to where he will be, so try to always be on the move.
Poison is very effective. Poisoning multiple segments essentially stacks the poison effect, dealing a lot of damage relatively quickly. Pin has six body segments, meaning you can stack it on it many times.
Piercing attacks, such as Technology and Cupid's Arrow, are devastating if fired at Pin horizontally, as each body part takes damage separately. Splash damage (bombs, IPECAC, etc.) will also have a similar effect, and due to Pin's low health, a well-placed bomb can kill Pin at full health.
Using Mom's pad against Pin causes him to separate and the segments will get very far apart until the effect wears off.
Dead Bird is very effective if Isaac can get it near Pin.
Pin is larger, and fires six shots in all directions rather than an explosive shot when it pops its head out of the ground. In addition to coming out of the ground faster,all the shots that it fires have a higher velocity.
Eternal Pin looks longer (8 segments instead of 6), dives faster and more often. It constantly shoots blood shots to both sides throughout its jump, but its tail no longer shoots. Its secondary attack launches 5 to 6 IPECAC shots which leave damaging creep.
While Wrath of the Lamb featured many dead versions of old bosses, Pin is the younger version of Scolex. It attacks and behaves nearly exactly like Scolex but can be damaged from any side, instead of just the back.
Pin shares with Scolex a similarity to the The Legend of Zelda boss Lanmola, though Pin is perhaps even more similar, firing shots in an identical manner to The Legend of Zelda boss when emerging from the ground.
Pin is most likely based off of the Pinworm, an internal parasite that lives in feces and can be consumed in unwashed vegetables. They are common in young children, but are usually harmless to humans.
When firing an IPECAC shot, the sound Pin makes is the same as the sound Suture makes when it becomes enraged.
If struck by an attack that freezes or slows down mid flight (eg. Mom's Bra), Pin will fall straight down.
Pin will frequently damage itself with its explosive shots, especially if the player is close to it when it pops out of the ground.
Sometimes in the credits, Scolex will be rapidly flashing between Pin and Scolex's appearances.
After using its secondary attack (with the explosive shot), Pin disappears into the ground and cannot be seen, but shots fired at that location will still hit and hurt it.
After using the secondary attack Pin will always jump out of the ground on that spot.
If Pin is dealt the finishing blow by the Dead Bird, it will instead revert to full health and will have to be killed again. After this, the rumbling dirt animations that play when it leaps out of the ground will no longer show.
If Isaac use Mom's Pad while Pin is in mid-flight, all of his segments will separate and go to different places, trying to get away from you (including the hole he comes out of).
If Pin is killed while jumping directly over the item spawn area, the item may disappear.