Blox Fruits Prison Secret: Cell Block Key and Don Megalo’s Cloak

The Prison in Blox Fruits’ First Sea holds a small chain of actions that ends with a Level 250 boss standing between you and a stolen coat. It starts with a key nobody points you toward, and it finishes at the top of the tower keep in a cell that does not look like a cell at all.

Quick answer: Take the Cell Block Key off the wooden planks directly behind the Warden, climb the ladders to the top of the prison tower, use the key on the gated door, then interact with the blue cloak on the stand inside Don Megalo’s cell. Grabbing it spawns the Megalo Guard, a Level 250 boss.

Cell Block Key: What it is and what it opens

The Cell Block Key is a pickup, not a quest reward. No NPC hands it to you and no dialogue prompt mentions it. It sits in the open on the ground floor of the Prison, and it has exactly one use.

Detail	Value
Item	Cell Block Key
Where it sits	Wooden planks directly behind the Warden
Island	Prison, First Sea (Level 190–250 area)
What it opens	The gated door at the top of the prison tower
Behind the door	Don Megalo’s cell, built like a penthouse suite
Trigger inside	Taking the blue cloak from its stand
Spawns	Megalo Guard, Level 250 boss

Where to find the Cell Block Key behind the Warden

Dock at the Prison and head through the main gate into the grassy courtyard. The Warden patrols this area along with the island’s other bosses, so give yourself a moment to spot him rather than sprinting straight past.

Sweeping the Prison courtyard to locate the Warden. Image: Gamer Robot Inc.

Walk up behind the Warden and look at the wooden planks propped there. The key rests on top of them with a Take prompt attached. You do not need to fight the Warden first, and you do not need any quest active.

Interact with it. A confirmation reading Picked up the "Cell Block Key" appears on screen. That message is your proof the pickup registered, so if you never see it, you have not actually taken the key.

Climbing the prison tower and unlocking the gated door

Move to the small castle keep at the back of the courtyard, the one lined with spotlights. Everything from here happens vertically, so ignore the ground-floor rooms.

Approaching the tower keep after picking up the key. Image: Gamer Robot Inc.

Follow the ladders up through the tower’s brick passages until you reach the very top floor. There is no shortcut worth hunting for here; the ladders take you all the way.

Player moving along a marked route through a brick-walled passage inside the prison tower — The route up through the tower’s interior passages. Image: Gamer Robot Inc.

Stand in front of the gated door at the top and use the Cell Block Key. The gate opens on the spot. Behind it is a short flight of stairs leading into the cell.

Inside Don Megalo’s cell: Taking the cloak

The room is furnished more like a suite than a holding cell, and the bed is empty. Your character reacts to it out loud, working through the obvious conclusion: the Warden was not locking Megalo up, he was keeping him comfortable, and Megalo is no longer here.

This is Don Megalo’s cell…? It looks more like a penthouse suite! And the bed’s empty.

The blue cloak sits on a stand in the room. Interacting with it is the actual trigger for the secret, and it cannot be undone once you press it.

The interior of Don Megalo's cell at the top of the prison tower — Don Megalo’s cell, furnished like a suite, with the cloak on display. Image: Gamer Robot Inc.

Megalo Guard boss fight and the death penalty

The moment the cloak leaves the stand, the Megalo Guard appears and calls you out. He is tagged as Megalo Guard [Lv. 250] (Boss), which puts him at the ceiling of the Prison’s level band.

Hey! Put that down! That coat belongs to the boss. You don’t touch what’s his.

Player standing inside the tower room as the Megalo Guard encounter begins — The Megalo Guard confrontation triggers inside the cell itself. Image: Gamer Robot Inc.

Note: dying to him costs you 250 Bounty, since the game applies its standard NPC death penalty here. The fight happens in a cramped room at the top of a tower, so there is very little space to kite him. Turning up around Level 134 with roughly 225 health is not enough, and the walk back up is not short.

Why the secret does not trigger

There are only a few points where this breaks down, and each one has a clear tell.

The gate will not open. You have not collected the key. Return to the Warden and confirm the pickup message appeared.
You cannot find the key. It is on the wooden planks behind the Warden specifically, not near the Chief Warden or Swan.
No dialogue plays in the cell. You need to climb the stairs past the gate and enter the room properly before the lines fire.
No boss appears. Only interacting with the cloak on its stand spawns the Megalo Guard. Walking through the room does nothing.

If you die, you respawn outside the tower and the climb resets, but the key stays with you. Come back at a level where a 250 boss in a confined room is a fair fight rather than a formality.