This is a great standard moveset! Coverage, STAB, buffing, and recovery! I must say, Cresselia is my favorite legendary.
If you're interested, Cresselia can also utilize a straight sweeper set, and a full support set:
SWEEPER (Needs Baton Pass support for Speed/ Special Attack. Works in perfect synergy with Girafirig):
Shadow Ball (Coverage against Ghosts and other Psychics)
Signal Beam (Coverage against Darks, Psychics, and even Grass-types)
Psychic (Obvious STAB. This and Shadow Ball lower Special Defense for improved sweeping)
Ice Beam (Coverage against Dragon, Flying, Grass, and Ground-types)
SUPPORTER / DUAL-SCREENER:
Reflect (Screens and adds Defense for the team)
Light Screen (Screens and adds Special Defense for the team)
Moonlight (Reliable recovery in case you need to set up screens again)
Lunar Dance (When Cresselia's about to faint, use this to fully restore that fainted Sweeper. Works incredibly in any team)
Cresselia makes an incredible supporter, and with its enormous bulk and already passable offensive stats, it can do anything, with the right Baton-Passer support. The only problem with Cresselia is that, for a legendary, its movepool is pretty shallow (Ice Beam, but no Thunderbolt? Epic fail...), so make the best out of what you have.