When your opponent activates a Spell/Trap Card, or monster effect, while you control a "CXyz" monster, or a monster with "Number C101" through "Number C107" in its name: Negate that activation, then you can attach 1 monster from the field or either GY to 1 Xyz Monster you control. You can banish this card from your GY; Special Summon 2 "Umbral Horror" monsters from your GY. You can only use 1 "Barian's Seal" effect per turn, and only once that turn.