Echo

Echo is a keyword ability on permanents that requires the permanent's controller to pay its echo cost at the beginning of the player's next upkeep after he or she gains control of it, or sacrifice it. Echo first appeared in the Urza Block, but has since been revisited in the Time Spiral Block.

In the Urza Block, echo meant "At the beginning of your upkeep, if this permanent came under your control since the beginning of your last upkeep, sacrifice it unless you pay its mana cost," but this was changed in Time Spiral by instead giving all echo cards an "echo cost" that has to be paid to avoid sacrificing the permanent. This gives echo more potential design space, as it means cards can have an echo cost that is different to their mana cost. All Urza Block cards with echo have now been given errata to give them echo costs equal to their mana costs.

From the Comprehensive Rules

• 502.19. Echo
  • 502.19a Echo is a triggered ability. “Echo [cost]” means “At the beginning of your upkeep, if this permanent came under your control since the beginning of your last upkeep, sacrifice it unless you pay [cost].”