Another extension of Yuri’s mind control technology, the Master Mind vehicle is capable of safely mind controlling a large group of enemy units at a time. However, this unit can’t stop itself from mind controlling additional enemy units. Exceeding its unit limit causes the device to break down and self-destruct, releasing all of its formerly captured units. - Red Alert 2: Yuri's Revenge manual(src)
The Mastermind is particularly deadly when deployed in the middle of enemy forces where they can cause mayhem in the enemy ranks. This ability makes it potentially devastating to an otherwise unstoppable armoured column before they make their mark on the battlefield. One major weakness with this weapon system however, is its lack of self-defensive armament. This makes it completely helpless against units immune to psychic control such as terror drones, robot tanks and air units when airborne. As mentioned above however, its greatest weakness is that it is prone to burning out when it has too many units under its control. This led to the tactic of rushing the Mastermind with many cheap and fast units such as conscripts, flak tracks or IFVs. Paratrooper conscripts are ideal for this task as they are both free and plentiful. Yuri's Masterminds can control up to 3 units each without going into overdrive.
When the Mastermind has mind controlled too many units, it will take damage every 60 frames (or 4 in-game seconds). The more mind control victims, the more damage it receives.
Takes 50 damage every 30 frames if 4-6 units are mind controlled.
Takes 100 damage every 60 frames if 7-10 units are mind controlled.
Takes 500 damage every 60 frames if 11 or more units are mind controlled, effectively destroying it instantly no matter its current health; if it collected an Armor crate, the damage is halved and it's possible to save it with Machine Shops and/or Repair IFVs.
Masterminds controlled by the AI have the following attack patterns:
1x targeting vehicles, accompanied by 2 Lasher Tanks and 1 Gattling Tank.
1x targeting vehicles, accompanied by 4 Yuri Clones and 2 Gattling Tanks.
1x targeting base defenses, accompanied by 4 Brutes, 2 Lasher Tanks, 2 Gattling Tanks and 4 Magnetrons.
1x targeting vehicles, accompanied by 5 Lasher Tanks and 2 Gattling Tanks.
2x targeting vehicles, accompanied by 4 Lasher Tanks, 1 Gattling Tank and 1 Magnetron.
2x targeting vehicles, accompanied by 6 Lasher Tanks and 3 Gattling Tanks.
This strike force will only be constructed if the AI owns a Psychic Dominator.
I am the Mastermind.
Enter the think tank.
A mind is terrible thing to waste.[sic]
Alpha wave ready.
Let's have a meeting of the minds.
Mastermind on the move.
Let's make some friends!
We're on diplomatic mission![sic]
Where are the simpletons?
Always looking for new ideas!
When ordered to attack
Time for a brain storm!
This will be painless!
Come into the fold!
They will understand.
Their mind will be addressed.
Let's collect our thoughts.
According to the concept art for the Mastermind, the scaling of the vehicle shows that the brain is twice the size of a tank.
It is possible to lengthen a Mastermind's lifespan indefinitely even when it has mind controlled too many units (more than 10) by means of IFVs with Engineers inside them to repair it and collecting an Armor crate. Note that the Mastermind needs to be completely surrounded by these IFVs, leaving either party vulnerable to enemies immune to mind control (e.g. Terror Drones and Robot Tanks).