I'm not sure Winter Orb is that #1 card for a sideboard slot, seems pretty weak imo.
Winter orb is very good in the SB of UR delver, against miracles / lands / eldrazi / BUG or any strategy that have some density of 2 mana or more spells and no mana dork.
try it and u will like. at least if you have some quantity of miracles in the metagame.
Eldrazi aggro player
Working in MonoR welder/engineer painter deck
In love with CoTV and Legacy for so many years