Spawns a familiar which follows Isaac and picks up any nearby coins. Bumbo changes level based on the amount of coins it's collected.
Level 1 (0-5 coins): Bumbo just collects coins to level up.
Level 2 (6-11 coins): Bumbo occasionally drops a pickup, trinket, chest or pedestal item after a room clear.
Level 3 (12-23 coins): Bumbo now fires tears that deal 3.5 damage in the same direction Isaac does. Bumbo's tears have a chance to drop a coin if they hit an enemy.
Level 4 (24+ coins): Bumbo no longer fires tears and instead chases enemies slowly and deals contact damage (2.5 per tick, or 37.5 per second/10.7 per second). Bumbo will occasionally drop Bombs while chasing enemies or coins.
After reaching level 4, Bumbo will continue to collect coins, and can drop a pickup, trinket, or chest for each coin it collects, similar to Bum Friend.
Bumbo can also drop pedestal items.
Notes
Level 1-3 Bumbo can fly over pits and obstacles, despite having limbs at level 2 and 3 that serve him as legs.
If Bumbo consumes an absurd amount of coins while level four, Bumbo can become level one again (Unsure if bug, likely a buffer overflow)
If Level 4 Bumbo targets Mega Satan's head, Bumbo will attempt to "chase" him the entire fight by standing in the middle of the room.
Level 4 Bumbo's bombs are unaffected by Isaac's bomb synergies.
Bumbo cannot pick up Sticky Nickels and will hover over them. Level 4 Bumbo can eventually bomb the Sticky Nickel to free it.
Bumbo will pick up Lucky Pennies, without additional benefit to evolution or drops.
If Bumbo drops a pedestal item, it will be pulled from the current room's item pool.
Bumbo's level is reset when entering the Knife Piece 2 sequence.
Level 4 Bumbo can target charmed enemies and will try to follow them around to no effect. This prevents him from picking up coins until the target is changed.
From a scoring perspective, Coins that Bumbo picks up count towards your Schwag bonus on daily runs. (only applies to Afterbirth and Afterbirth ✞ dailies)
Synergies
BFFS!: Doubles both the contact and shot damage, when applicable.
Interactions
Box of Friends: Will spawn a level 1 Bumbo regardless of the original Bumbo's current level.
Bum Friend: The bum friend will follow Bumbo instead of Isaac.
Keeper: Not recommended, as the coins Bumbo collects could have been used to heal Keeper.
Tainted Keeper: Due to the large influx of coins spawned, it's technically possible to sustain Bumbo while also maintaining a good level of wealth and health.
Collision between Bumbo and other bum familiars such as Dark Bum can prevent them from collecting pickups if you're holding one of the firing buttons upon entering a room
Level 1 (0-5 coins): Bumbo just collects coins to level up.
Level 2 (6-11 coins): Bumbo occasionally drops a pickup, trinket, chest or pedestal item after a room clear.
Level 3 (12-23 coins): Bumbo now fires tears that deal 3.5 damage in the same direction Isaac does. Bumbo's tears have a chance to drop a coin if they hit an enemy.
Level 4 (24+ coins): Bumbo no longer fires tears and instead chases enemies slowly and deals contact damage (2.5 per tick, or 
37.5 per second/
10.7 per second). Bumbo will occasionally drop 
Bombs while chasing enemies or coins.
Bum Friend.
Mega Satan's head, Bumbo will attempt to "chase" him the entire fight by standing in the middle of the room.
Sticky Nickels and will hover over them. Level 4 Bumbo can eventually bomb the Sticky Nickel to free it.
Lucky Pennies, without additional benefit to evolution or drops.
Knife Piece 2 sequence.
Bumbino.
BFFS!: Doubles both the contact and shot damage, when applicable.
Box of Friends: Will spawn a level 1 Bumbo regardless of the original Bumbo's current level.
Keeper: Not recommended, as the coins Bumbo collects could have been used to heal Keeper.
Tainted Keeper: Due to the large influx of coins spawned, it's technically possible to sustain Bumbo while also maintaining a good level of wealth and health.
Bug!
Ashpit/
Mines II.
Dark Bum can prevent them from collecting pickups if you're holding one of the firing buttons upon entering a room
The Binding of Isaac: Rebirth
