Hi!
Mercenary passive Nowhere to Hide most interesting part is Mark of the Diablo. It should prevent target from reviving and gaining beneficial effects. It should be great against the most popular Eddie in top Arena - Maxed Cyborg wearing sacred/serenity/Cyborg Cosmic. It doesn't work. Cyborg keeps getting beneficial effects.
I did screenshots. Mercenary attacks. Its basic removes all buffs from Cyborg but Cyborg still gets some buffs.
Silmilar things happens when attacking other chars also.
I got Application hanging on my phone when I was testing Mercenary against Mystic (Celestial)M Lilith( Limbo ) Madame ( Alchemy ) Charlotte (Viper/Freeze). This hanging I couldn't reproduce on other device. Mark of the Diablo should prevent reviving, but when this triggers is unclear. Cyborg's passive managed to revive Mushashi killed under the Mark of the Diablo.
Overall Mercenary is not so great. Probably most useless Gauntlet prize char so far. Char so hard to get should have at least a little use in Arena. It does not. Mercenary is not a team player at all. Its basic is single target attack. To use its full potential it needs bleed inflicted. Good luck with that! If you even get that bleed on some Arena char it will be cleaned anyway before next turn. And building up team around Mercenary is lost cause. Its power move is single attack too, it cleans, heals and gives buffs only to Mercenary itself. Its passive gives buffs to everybody but only at the start of the battle and most top chars will remove those buffs at once. Killer's hidden Passive Disable kills that too. Mercnary gets its passive disabled so easily! And if this happens all Marks of Diablo are gone. Mark of the Diablo could be great if it works. Mercenary is currently nice trophy char, nice to look at but lonely sad man in battlefield. To be useful it should clean silvers from all team. Or it could get new turn if it manages to inflict bleed. Or it should be immune to passive disable.
P.S
Moonchild disables Mercenary power move also. It should not happen.