Most Physical STAB Fighting moves will take it out or do a huge chunk. I know that Landorus-T's Choice Band Superpower utterly destroys it.
Not many can OHKO it though, says Smogon:
>Despite Chansey's titanic defensive capabilities, physical Fighting-type attacks will still deal catastrophic damage to her, though few are capable of OHKOing the Egg Pokemon.
I was still editing, Leboss :P
Anyway, an Adamant Choice Band Infernape OHKOs, Joly ones do not. Choice Band Terrakion and OHKO with Close Combat.
Well, here's your edit.
No Special move is going to make a dent in Chansey, anyway. I took the strongest Special move possible that does damage to Chansey's defense stat, Psystrike. I gave Mewtwo a Choice Specs, made it Modest. Does not OHKO. I also took Deoxys-A with Psycho Boost. No OHKO, same setup as above. I also took a Porygon-Z with the same setup, with Hyper Beam Adaptability. No OHKO. Here are the stat calcs.
252SpAtk Choice Specs Unnerve Mewtwo (+SAtk) Psystrike vs 252HP/252Def Eviolite Chansey (+Def): 57% - 67% (405 - 477 HP). Guaranteed 2HKO.
252SpAtk Choice Specs Deoxys (+SAtk) Psycho Boost vs 252HP/252SpDef Eviolite Chansey (+SpDef): 31% - 37% (225 - 265 HP). Guaranteed 4HKO.
252SpAtk Choice Specs Adaptability Porygon-Z (+SAtk) Hyper Beam vs 252HP/252SpDef Eviolite Chansey (+SpDef): 36% - 43% (258 - 304 HP). Guaranteed 3HKO.
No OHKOs. Sorry.
