B.O.B. is the latest invention of Master Builder designed to work as the 6th Builder in the Home Village, replacing O.T.T.O. Unlike the five initial builders you buy with gems, unlocking B.O.B. takes a lot of time and effort. So today, we will explain how to unlock the sixth builder in Clash of Clans.
Build the B.O.B. Control

B.O.B. Control is a building in the Builder Base. To unlock it, spend 1,00,000 Gold once you reach Builder Hall level 9. However, players will have to upgrade the B.O.B. Control to level five to unlock the sixth builder.

To upgrade B.O.B. Control, you need to fulfill four prerequisites listed below:

Gear Up 3 Buildings in the Home Village
The first task is to gear up these three buildings: Cannon, Archer Tower, and Mortar. For this, you need a level seven Cannon in Home Village and a level four Double Cannon in the Builder Base.

Similarly, you'll need a level 10 Archer Tower in the Home Village and a level six Archer Tower in the Builder Base to gear up the Archer Tower. Lastly, you need a level eight Mortar in Home Village as well as a level 8 Multi Mortar in the Builder Base. Make sure to upgrade to Town Hall level 10 beforehand to ensure all these upgrades are possible.

Upgrade Any Troop to Level 18
For this step, you first need to upgrade your Star Laboratory to level nine, and then choose any character that you use the most and upgrade it to level 18. It is recommended, however, to upgrade either Baby Dragon or Power P.E.K.K.A. for maximum efficiency, but it's really up to you to choose which troop to upgrade.

Upgrade Any Builder Base Defense to Level 9
The quickest way to complete this step is to upgrade your Multi Mortar by spending 4.5 Million Builder Gold. In the past, players used to upgrade a wall to level nine as a workaround, but it does not work anymore.

Upgrade the Battle Base Heroes to Level 45 Combined

There are two Battle Base Heroes: Battle Machine and Battle Copter. The easiest way to achieve a combined level of 45 is by upgrading the Battle Machine to level 25, which will unlock Battle Copter. The initial level of Battle Copter is 15, which means only five more upgrades would bring it to level 20 and complete this step.
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Upgrade the B.O.B. Control and Unlock B.O.B.'s Hut
As you complete each task, you can upgrade your B.O.B. Control by one level until you reach level five and unlock B.O.B's Hut. After that, place the hut in the Home Village to get your 6th Builder in Clash of Clans.