Yes, it's true, Sega and Rovio have joined forces for a special three week-long in-game event. It sees Angry Bird Epic invading Sonic Dash.
Each week of the event, one of the Angry Birds will be unlockable as a playable character in Sonic Dash to make three in total.
All you have to do is collect the Angry Birds character tokens while running through levels in Sonic Dash. Or, if you prefer, you can purchase them with premium currency for the duration of the event.
As this is Angry Birds Epic and not regular Angry Birds, the three characters are in their fantasy forms. So you get Red as a Knight, Chuck as a Mage, and Bomb as a Pirate.
And don't worry, once you've unlocked the Angry Birds they'll be playable in Sonic Dash after the event has closed.