Is Clockwork Avian legal in Standard, Modern, and Commander?

Clockwork Avian is legal in: Legacy, Vintage, Commander.

What type of card is Clockwork Avian?

Clockwork Avian is an Artifact Creature — Bird. Its oracle text reads: "FlyingClockwork Avian enters with four +1/+0 counters on it.At end of combat, if Clockwork Avian attacked or blocked this combat, remove a +1/+0 counter from it.{X}, {T}: Put up to X +1/+0 counters on Clockwork Avian. This ability can't cause the total number of +1/+0 counters on Clockwork Avian to be greater than four. Activate only during your upkeep."

Clockwork Avian

Artifact Creature — Bird

Flying<br>Clockwork Avian enters with four +1/+0 counters on it.<br>At end of combat, if Clockwork Avian attacked or blocked this combat, remove a +1/+0 counter from it.<br>, : Put up to X +1/+0 counters on Clockwork Avian. This ability can't cause the total number of +1/+0 counters on Clockwork Avian to be greater than four. Activate only during your upkeep.