No idea what the snowman debuff does but basically just gave me free turns if anything. Logged on early enough to do Ragnarok before reset. No problems using my light team and again with my thunder team using Gawain+Sniper. Didn't really pay attention but I think regular overdrive for ragnarok inflicts atk down, double atk down and triple atk down.
And not that it really matters but trash mobs are dark for the other difficulties.
Also very nice log in rewards.
Overall event, very easy.