The thirty seconds starts as the ability starts resolving and you start lauding. Someone should be ready to time you before you activate the ability.
2022-10-07 • wotc
Lauding means singing the praises of the creature in question. Complimenting it. Telling everyone of its awesomeness, that kind of thing. Don’t stray off-topic. And resist the urge to say “Please clap”—86% of audiences don’t respond well to desperation.
2022-10-07 • wotc
“Only once” means once for that particular creature. If a different copy of Carnival Barker enters the battlefield, or if Carnival Barker leaves the battlefield and returns, it’s a new object and its ability can be activated. Please be considerate of others around you before designing a deck around blinking and activating Carnival Barker three times each turn.
2022-10-07 • wotc
If another player gains control of a Carnival Barker whose ability has been activated, they won’t be able to activate it. That Barker’s all barked out.
2022-10-07 • wotc