digimon tcg booster box [EX05] Animal Colosseum 1 Box topper pack incorporates survey responses from both English ver players and Japanese ver players BANDAI | Digimon Card Game:

Thats because Beast Within costs three mana, is an instant and can target any permanent

Main Deck 40 Forbidden Cards Forbidden Fossil Dyna Pachycephalo X EARTH Level 4 [ Rock / Effect ] ATK 1200 DEF 1300 If this card is flipped face-up: Destroy all Special Summoned monsters on the field

As for the effect, it was evaluated at the time that it was a very plain effect with a canosol that has a limit on the number of times and attacks, but the damage is 1000, which is unexpectedly ridiculous

If youre a Pokemon TCG collector and you arent sure whether to get some Mask of Change Booster Packs or not, it could be worth looking up the full card lists to get a better feel for the set