Summons a ghost near Isaac that will follow him around, and summons a controllable blue crosshair. After a few seconds, the crosshair disappears, and the ghost will act depending on what the crosshair was targeting:
Enemies: Attacks the enemy until it dies or can no longer be targeted due to a form change or similar cause. The ghost does 3 damage per tick, for 9 damage per second.
Doors: Opens the door, even if it is locked. Functions the same as Dad's Key when being used in this way. This includes the door to Mega Satan, exiting Hush's room, and exiting Boss Rush.
This does not work on A Strange Door. However, it does work on doors leading to alternate path levels.
If the room has nothing to interact with, the ghost will disappear without doing anything.
Notes
If the crosshair is not targeting anything when the crosshair disappears, the ghost will interact with the object closest to the crosshair.
Picking up a stolen Devil deal will not prevent Angel Rooms from appearing. It will also not despawn the other Devil items for characters like The Lost.
The ghost cannot pick up Sticky Nickels and will disappear upon touching them.
The ghost can open chests in Challenge Rooms without triggering the room.
Unlike chests, stealing an item pedestal from a Challenge Room will trigger the waves to spawn upon picking up the stolen item.
In rooms with multiple pedestal items where only one can be taken, if the ghost is carrying a pedestal while Isaac picks up a different pedestal item, the ghost will disappear. This prevents taking both items for free.
If used in an Angel Room with no item pedestals, Mr. ME! will target the angel statue, blowing it up.
If used with MouseControl=1 enabled, while pressing mouse left button, the blue crosshair will keep going away from the character, not following the mouse.
Having Marked make the blue crosshair follow the mouse instead.
Synergies
Book of Virtues: Spawns a wisp that looks like a face in the middle ring. The wisp cannot shoot. If the current room is cleared, the wisps automatically move toward and unlock chests (Except for Bomb Chests and Mega Chests) and special room doors, destroying themselves in the process. The wisps can open almost any locked doors, including the ones to Mega Satan, the Ascent, but excluding Corpse.
Interactions
BFFS!: Does not increase the ghost's damage when attacking enemies.
Car Battery: May sometimes glitch pedestal items, resulting in Isaac being unable to pick them up without leaving and re-entering the room. Otherwise has no effect.
If used while shooting with Marked, the crosshair will continue straight in the first direction Isaac shot at, and cannot be controlled until Marked is deactivated.
Bug!
Mr. ME! is able to damage Mom's doors even when no body part is sticking out of them, Mom's Heart and It Lives while they're withdrawn, and Isaac and Hornfel while they're off-screen. He never loses them as a valid target, eventually killing the boss.
Bug!
If attempting to explode an angel statue using Mr. ME! after ??? or The Lamb have been killed, the game will result in a crash.
Trivia
Mr. ME! is based on this Steam Workshop item by Jean-Alphonse, originally known as Mr. Meeseeks.
Mr. ME! is a reference to Mr. Meeseeks from Rick and Morty, which spawn from a box and stop existing after completing their given task.
The pickup quote also refers to a catchphrase used by Mr. Meeseeks.
Chests / 
Red Chests / 
Spiked Chests / 
Mega Chests: Brings it to Isaac. Can steal from 
Shops, 
Devil Rooms, and 
Black Markets, making the item/pickup free. Stealing an item has a 50% chance to fail. If that happens, a buzzer sound will play and the ghost will disappear without doing anything.
Stealing an item from a Shop will restock it with another item, as if Isaac had 
Restock. This does not happen in other room types.
Locked Chests / 
Eternal Chests / 
Bomb Chests: Opens the chest for free.
Pressure Plate/ 
Reward Plate: Presses the button. This includes the wave pause button in Greed Mode.
Dad's Key when being used in this way. This includes the door to 
Mega Satan, exiting 
Hush's room, and exiting 
Boss Rush.
A Strange Door. However, it does work on doors leading to alternate path levels.
Mom's Heart that appears after defeating 
Mom in 
Mausoleum or 
Gehenna.
Home to unlock the tainted characters.
Secret Room entrances: Explodes, opening the entrance.
Shopkeepers, 
Slot Machines, 
Beggars, and 
Angel Rooms from appearing. 
The Lost.
Sticky Nickels and will disappear upon touching them.
Challenge Rooms without triggering the room.
Marked make the blue crosshair follow the mouse instead.
Book of Virtues: Spawns a wisp that looks like a face in the middle ring. The wisp cannot shoot. If the current room is cleared, the wisps automatically move toward and unlock chests (Except for 
Corpse.
BFFS!: Does not increase the ghost's damage when attacking enemies.
Car Battery: May sometimes glitch pedestal items, resulting in Isaac being unable to pick them up without leaving and re-entering the room. Otherwise has no effect.
Flip: Ghostly items cannot be targeted.
Sack Head: If Mr. ME! successfully stole a consumable from the shop, there is a chance he will drop a sack instead.
Bug!
It Lives while they're withdrawn, and 
Isaac and 
Hornfel while they're off-screen. He never loses them as a valid target, eventually killing the boss.
??? or 
The Lamb have been killed, the game will result in a crash.
The Binding of Isaac: Rebirth
