Echo

Echo is a keyword ability on permanents that requires the permanent's controller to pay its echo cost at the beginning of their next upkeep after they gain control of it, or sacrifice it.

Description
Echo first appeared in Urza's block, but has since been revisited in the Time Spiral block and Modern Horizons.

In the Urza's 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 from their mana cost. All Urza's Block cards with echo have now been given errata to give them echo costs equal to their mana costs. However, the return of echo in a Standard set is unlikely as it's not a very popular mechanic. According to Mark Rosewater, players don't like downside mechanics unless they're especially flavorful, and echo is about as unflavorful as it gets.

Rulings

 * Paying for echo is always optional. When the echo triggered ability resolves, if the controller of the permanent can't pay its echo cost, or chooses not to, that player sacrifices that permanent.
 * A permanent's echo ability will trigger during its controller's upkeep if it came into play since the beginning of its controller's last upkeep (including if it left play and came back during that time), or if its current controller took control of it since the beginning of their last upkeep.

Creature that reduces Echo costs

 * Thick-Skinned Goblin