The speaker describes a moment of watching other people react to them: one person's eyes go dim, one cries, one huffs, and another just stares. The Scooby-Doo image is the key. The speaker feels like those onlookers are waiting for a mask to be pulled off, as if the real person underneath will turn out to be someone more familiar or acceptable. The speaker half-expects that after a couple more tries, they'll be "back to being me," which sounds tired and a little sarcastic, as though they're being asked to perform a version of themselves for others' comfort.
Then the poem turns sharply at "but." The tone shifts from weary observation to bitterness. Promises are called "empty words," and the people who made them are "temporary fill-ins," meaning replaceable and not truly committed. The mood is hurt and guarded, with a dry humor on the surface. The title, "Ancient Artifact," suggests the speaker may feel like a relic of something long gone, or that these broken promises are old wounds.