Q. about R'Lyeh Mind Blast

[Crazy]

I am playing R'Lyeh for the first time and have a few questions.

Many units have a melee attack and mind blast.

Does this mean that they can attack with their weapon, like trident, AND mind blast??

If I set their orders on FIRE will they stay back and only mind blast?

If I set to attack with they ONLY attack hand to hand?

What is the best tactic? Setting them as far away from the enemy as possible to give them as many mind blasts as possible before engaging?

Also, does mind blast do damage or just kill enemy?

Thanks.