“Use the Arc Energy to disrupt the Restorative Mind, and then destroy it.”
Theosyron, the Restorative Mind can be a difficult boss. This encounter takes time because of its various elements. As much as possible, aim for the Eye. This does significantly more damage than shots to anywhere else on its body. Take the body shots while moving into a better position to shoot.
First, it will protect itself at times with its shell. To get around the shell you will need to collect and use the Arc energy to disable this shell. You will need to open its shell any time you want to inflict damage.
When it shields itself, it will call in a number of Vex. These are very helpful to recharge your Super to bring against the Restorative Mind.
The second thing that makes this fight more difficult is after you cross the mid-point in the battle. The barriers on the sides of the room will start to move back and forth. This can catch ammo drops behind them, making them inaccessible. The Vex are unaffected by the barrier's movements but Guardians are pushed. More than anything, you will need to watch out for the stone pillars which you can get caught behind a crushed. You will also need to wait for the barrier once in a while
In the final part of the battle, the Restorative Mind will start using the Medusa's Stare. When it starts doing this, will have moved back into the middle portion of the chamber or be in the process of it. If you see "Spotted" displayed below the countdown for the Stare, get behind a pillar. When the countdown hits zero, whoever is spotted is dead.
Survive through this part, fire on the Eye of the Restorative Mind and it will not be too long before it is destroyed.