You can use it as a sort of protective spell by responding to an opponents removal spell and copying the creature they attempt to kill, or surprise a creature like Niv-Mizzet, Parun in combat to trade
This will not work in response to a battle, only a card effect
the damage you take from that battle is halved
Several factors influence Base Set 2 card values: card condition (mint cards worth 3-5x more), rarity (holographic and rare cards command higher prices), first edition status, PSA/BGS grading scores, and market demand for specific Pokemon
beyond being holographic, itll look pretty much the same as a Common or Uncommon card though the cards Pokemon or Trainer card abilities are likely to be pretty useful in-game
Gladiator Beast Vaspasius might be an Effect Monster, but since its WATER, it can be used as the cost to banish for activating the effect of Sea Stealth Attack that protects your face-up Spell & Traps from being destroyed by your opponents effects, while also allowing you to more easily achieve the conditions of activating the effects of your Phantasm Sprial Trap Cards