I run this Latias set, with different evs from the one in this thread:
Latias (F) @ Soul Dew
EVs: 252 HP / 64 Def / 192 Spd
Timid Nature (+Spd, -Atk)
- Calm Mind
- Dragon Pulse
The HP and defense investment helps Latias survive priority, and Psyshock 2hkos Arceus-Steel at +6 which is nifty, even with no investment.
A few general checks to Latias: arc steel, arc dark, arc ghost, arc rock, mold breaker exca, payback/toxic forry, ho-oh, lugia, physical scarfer, scizor, tyranitar, extremespeed/shadow sneak, mix palkia
Just felt like throwing in my two cents.