Paying 1000 Life Points is a cost to activate the effect of "Master Gig". This effect does not target.
You determine the number of destroyed monsters based on the number of face-up Psychic monsters you control when this effect resolves.
If the number of monsters controlled by the opponent is less than the number of face-up Psychic monsters you control, you cannot activate the effect of "Master Gig". If the effect has already been activated and you control more Psychic-Type monsters than your opponent has monsters when the effect resolves, you cannot destroy any of the opponent's monsters.