JohnSnow
Hero
Arabesu said:Yes except that wizards can knock someone, many targets actually, prone at first level at range 10: Icy Terrain.
It doesn't specifically say so, but there is NO mechanical reason why it shouldn't work against a flier. Of course, your GM may rule that the power's intent, i.e. icy ground, prevents it from working unless the opponents are standing on the ground, but RAW that would be a houserule.
Flavorwise, it actually makes sense. The wizard issues a blast of icy air that would, naturally, make it hard for a flying creature to flap it's wings.
However, the secondary effect of "difficult terrain" doesn't matter because "Creatures are not hampered by difficult terrain when flying." (PHB, p. 284).
So you can knock them prone. Of course, by the time flight is common, it's pretty unlikely you're still holding on to "icy terain."