As Dinomorphia can easily get to 100 LP, "Rex" will practically become a Skill Drain, and, as a bonus, it may even reduce the ATK of enemy monsters significantly
Like most Pokmon cards, the value of Froslass ex depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Paradox Rift)
I do love love the Team Rocket set, and I do think the fact that it was the first set to feature Dark cards makes it somewhat unique, but the fact that there are no rookie cards combined with the fact that many of the species (Arbok, Slowbro, Vileplume, Hypno, Weezing, etc.) that landed holos in this set just arent very popular species in general lessens its overall luster
This means that many decks that can struggle to take down Pokmon with 250 or more HP can now easily do so, making Maximum Belt a phenomenal option to use if the meta is full of high HP Pokmon that can disrupt the board before a player is set up