Echo

Echo is a keyword ability that first appeared in the Urza block and recently in the Time Spiral block.

"Echo" used to mean "At the beginning of your upkeep, if this creature came under your control since the beginning of your last upkeep, sacrifice it unless you pay its mana cost." However, it was changed to be "Echo cost" and have a cost separate from the mana cost. All previous cards with echo received errata to be "Echo cost", where cost was the same as their mana costs.

No creatures before Planar Chaos has an echo cost different from its mana cost.

Thick-skinned Goblin has the effect that lets its controller pay rather than pay echo costs for permanents controlled by him or her, or, in other words, simply don't pay echo costs.