Only a few things I think need improvement in terms of graphics:
1) the mines... the icicles (being icicles) are quite unclear and easily missed, could make it a bit clearer
2) The ult.. really needs to be bigger and fancier.. all i see is just a medium white blob go into the center and then disperse, even the original ult which ends with an explosion and bang is nicer
3) I don't know if this is just me but the snowball seems smaller than ziggs normal bomb, but the explosion it leaves behind is the same which makes it look a bit wierd
4) Otherwise I love the art

Ok after seeing the updated fiddles and Veigar update, I sure hope this is an early WIP Ziggs skin, becuase they are awesome where this does feel lacking as pointed by everyone above.

Please keep the flip that Ziggs does when jumping using his w. I know the new skin is supposed to have different stuff, but the flip is so.. ziggs. And no matter what the skin, it looks awesome So please reconsider its presence on Snow Day Ziggs

I'm up for giant snowball splattering on the ground. Just sayin'.

Ziggs Q seems fine. Similar enough to regular bomb.
The snowman on the W skill is awkward. Looks like a sprite with a flashing color inserted instead of an actual object in the game.
The mines are awesome, I like them.
Like I see other people noticing, Zigg's ultimate when it falls out of the sky looks puny; almost the same size as his Q.

I haven't noticed any problems with his movement or image, nice job on the skin.

I haven't had a chance to test it on the most recent patch, that patch being today, but it seems that when Snowday Ziggs is in game with Nami her basic animation is broken. Specifically her movement animation as well as her ult animation. It would appear that she would hit a target champion, but not actually hit them. Will do more testing...