>>13092554>>13092589>Rare and taking so long to search for.That's when you end up using something known as the Repel Trick.
Cryogonal is (During Spring, Summer, and Fall) a 5% chance to appear in B/W2 at level 57. However, if you take a Pokemon that's at level 56/57 and use a repel, you'll only encounter Onix, Cryogonal, and Durant.
Though I'll admit that in B/W, it's a lot more up to luck for Cryogonal considering more similar leveled Pokemon and such, so the issue is more valid in B/W.
