Magic: The Gathering First Edition was released to the world in 1993
You always want to have the right cards available at the right time to do the most good
Like most Pokmon cards, the value of Mewtwo LV.X 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 (Legends Awakened)
Mendicant Core, Guidelight Mendicant Core, Guidelight is a nice artifact build-around card, and very cheap at just 2 mana
First strike is an especially good keyword on red creatures due to the speed of the color
Card condition may be indicated by HP, MP, LP, and NM. These mean heavily-played, moderately-played, lightly-played, and near-mint. Condition is a huge price factor, and you can find a guide here