Hide and seek is the silenced pistol on. I have done the pistol challenge, grenade, rpg and car and shotgun (got 780 on the shotgun one) so far. Think there are 12 in all it tells you in the handbook.
Yeah I didnt use the pistol just kept running up and doing takedowns managed to score 450 i think.
I need to get back on this for those challenges and I have only done 4 I think.