Force of Will Force of Will, the best counterspell in Magic, is probably the single most important card in the whole of the Legacy format
Tron Lands The Tron lands, Urza's Tower, Urza's Power Plant, and Urza's Mine are pretty pants on their own, but they're strong when you use their powers combined (much like Voltron which, believe it not, is where this trio of lands gets its nickname)
But I dont think there are many Crucible of Worlds effects if you take into account only cards released in Duskmourn
(Artifacts, legendaries, and Sagas are historic.) Sage Project Whenever Havi or another legendary creature you control dies, return target legendary creature card with lesser mana value from your graveyard to the battlefield tapped
It had an even power level across the set and a diverse array of mechanics and archetypes for players to enjoy