welcome to rathe unlimited booster box Opening! for no matter where you run Flesh and Blood TCG Compendium

While this card is likely spiking for combo-based reasons, Umbral Mantles ability is unlikely the reason for the spike

Grimmsnarl #SV085 Pokemon Shining Fates Keep track of your collection value over time

If 'At the start of the battle' is stated in your Digimon's Appearance Requirements, and they have a special ability that states 'When this card makes its appearance', activate that special ability before activating other special abilities that state 'At the start of the battle' or 'during battle' (the person second to attack activates theirs first)

An opponent separates those cards into two piles

There's really no breakeven point with this card