Float and Snort are used to counterattack any action used against them, even if the action misses. Float is harmless, but Snort will remove that character from the battle.

Comet, Aera and Virus Powder are the other attacks Yans use. Comet will either Miss, deal very little damage, or will kill you outright (8,000+ damage). Virus Powder will deal less damage (about 2,000) and inflicts the Virus status. They tend to use this move just before they die so you have no chance of curing the status before the battle ends (unless Eiko has Guardian Mog). Aera is used very rarely, and does what you'd expect.