Originally Posted by Josh
Considering all three of those can know Ice Beam (which is more accurate, and has a chance of freezing), I wouldn't bother teaching them at all (unless you desperately need an Ice-type attack now).
Icy Wind is only 5% less accurate, and will always lower the opponent's speed if it hits, though.
Mew doesn't really need it - without STAB, the move won't do a huge amount due to a small 55 BP.
Dewgong is the slowest of the two Ice mons, so it'd probably benefit from the effect more. Articuno is definitely more of an attacker anyway.
However, it's in-game, so it doesn't matter a huge deal. These are just my opinions x]