Tankenstein is sentient and was never controlled by anyone.
Death Neziro is the villains' base of operations and Dr. Hinelar's final arsenal against the Megarangers.
Tankenstein is the final monster-of-the-week in Power Rangers in Space.
After being stabbed by its own sword, Hinelar triggered the self-destruct, forcing the Megarangers to take Grand Neziro into the air to protect their school from the explosion. They managed to escape seconds before the blast.
After being fatally stabbed by his own sword, he grabbed onto the Mega Voyager and leaped into the air just before exploding in an attempt to take the In Space Rangers with him. The Rangers managed to survive the explosion.
Death Neziro fought the Megarangers in their final episode.
Tankenstein was in the penultimate battle for In Space.