Which 6* mystic to R2?

Miloticshyam

I have a 6* duped og guillotine and unduped Tigra, and pulled a mystic gem from the deadpool bundle.Should I use it,If yes on who?.
P.S:I have a 5* r5 doom and r4 bwcv who will be r5 as soon as i can gather the rank up mats.