Most of the rarest MTG cards come from Magic's earliest sets (Alpha and Beta) and appear on the Reserved List, which Wizards of the Coast has promised never to reprint
These cards just increases the mana cost of your opponent's spells, and while Thalia, Guardian of Thraben is a symmetrical effect (it affects you too), it is an extremely good card to drop in Turn 1 or 2 while your opponents are trying to play mana rocks or ramp their lands
Its unclear as to whether he was the first to produce such a mash-up
8.4/10$0.23 Vastwood Surge Sorcery Kicker (You may pay an additional as you cast this spell.) Search your library for up to two basic land cards, put them onto the battlefield tapped, then shuffle
Aang, at the Crossroads Destined Savior
(1/24/2025) The Spirit token has the color and mana cost (and thus mana value) of the original card