Cast massive Dinosaurs, attack for huge amounts of damage, and bring the prehistoric pain
MulchMulch, Winding WayWinding Way, Cache GrabCache Grab, Commune with the GodsCommune with the Gods, and plenty more are card advantage fountains
This combination of demand and rarity makes Mana Crypt the 4th-most-valuable card outside the Reserved List, behind two cards from Portal: Three Kingdoms (Imperial Seal and Zodiac Dragon) and one (Grim Tutor) which was exclusive to a particular 1999 starter deck
Sidisi is a four mana black, green, and blue 3/3 that has you mill three cards whenever they enter the battlefield or attack
A three-mana planeswalker with two (2!) powerful plus abilities adds up to a very potent card and its likely that the only thing keeping Oko, Thief of Crowns from being the most powerful card in Standard is the dynamic duo of Golos, Tireless Pilgrim and Field of the Dead
It exiles, note