Lets set aside the argument of what would be better in Legacy (spoiler: Mind Twist), despite the fact that Dark Ritual, Ancient Tomb, and City of Traitors are all legal
Its ability depends on power, not mana value, so you can reliably get ultra-powerful combo pieces like Kiki-Jiki, Mirror Breaker out if you can get it to the bottom of your library
A bonus to a kill spell can be the difference between a foe focusing on your most valuable Merfolk (the MVM, if you will) to changing their mind and destroying one of your other opponents' critters instead
#40 Juggernaut - Golden Age It died so Hypnotic Specter could live
Dive into packs pulled from across decades of MTG history, including older, out-of-print sets you rarely see anymore
Its especially useful with effects that care about land types like domain or converge and has found a home in decks looking to combo off with Valakut, the Molten Pinnacle