The Iron Will Pokemon evidence can be mainly found in the Roaring-Sea Caves. You can also find more evidence at the Frigid Sea, specifically along the shore and on the island. Lastly when facing Peony’s house in Freezington, you can find one set of footprints underneath the tree to the left of Peony’s house. Once you collect 100% of the evidence, the rest of the footprints for that type of Pokemon will disappear. After you find 100% of the Iron Will Pokemon evidence and report back to Sonia, she will tell you that the Iron Will Pokemon can be found in the Frigid Sea! Travel to the island in the Frigid Sea to find Cobalion (level 70) wandering around. After you catch Cobalion, return to Sonia for a reward.
