In essence, you've got to use creatures to power it up with charge counters until it activates, at which point it becomes a powerful artifact creature in its own right
This adds a lot of value to graveyard disruption cards like Bojuka Bog, Relic OF Progenitus, and Ghost Vacuum, but it is bonkers when used in conjunction with blink and flicker effects
Drip-fed reveals of the cards built anticipation, with some standing out as power players and others featuring beloved Disney characters, increasing their appeal
That said, these crystals all threaten inevitability in a stalled out game
Funnily enough, 2021 features another callback to this period in Magic history besides Elite Spellbinder, with Caverns getting a reprint in Time Spiral Remastered