Finally, giving a Pokemon that loves to Sketch boosting moves Infiltrator is a questionable idea; screens should go a long way in assisting the rampage that boosting sets will incur.
There is already plenty that give boosting CAP2 sets trouble besides screens. Intimidate, Heatran, Jirachi, Hydreigon, Sucker Punch, burn, paralysis, revenge killing, et cetera, all stand in the way of a boosting CAP2. Screens, which are mainly seen on hyper offensive teams to give their sweepers the ability to set up, shouldn't be one of the many things that stop CAP2 in its tracks.
Speaking of which, Dusk said over IRC that he wasn't convinced that
Infiltrator is a solid flavor ability, so allow me to state my case some more.
One definitions of Infiltrator:
To pass (troops, for example) surreptitiously into enemy-held territory
This implies deception, which ghosts typically excel in. In addition, most of the arguments for cute charm refer to our mon's lore, that it deceives prey by alluring it. (paraphrasing here) That does refer to deception as one of CAP2's key traits, pointing directly to Infiltrator. To those who think that CAP2 isn't cute enough for cute charm or reads cute charm itself differently, Infiltrator is a solid alternative as an ability that represents CAP2's ability to deceive opponents into letting down their guard, playing directly into our ghost's hands.
Furthermore, why should a ghost, defined as not having a material body, have to be hampered by material barriers like reflect and light screen? By its very nature, a ghost like CAP2 should be easily able to bypass such screens. Thus, Infiltrator.
TL;DR
Quack! Deception, alternative to cute charm as ability that plays off of CAP2's lore, its a ghost and has no material body