Angryverse/Astrotrain

When Autobirds or Deceptihogs need to get anywhere on Piggy Island, and get there fast, Astrotrain is the 'bot to call! He has a shuttle mode, and a locomotive mode, and they neutered any semblance of a robot mode. Neato!

Commercial appearances
Astrotrain dropped Optimus Prime Bird off on Piggy Island so that the Autobird could shoot at some Bad Piggies. Angry Birds Transformers: Comic-Con trailer

Angry Birds Transformers
An uncommon instance of a full body-shot of Astrotrain in his train mode when a bot enters Astrotrain in slow-motion in the Cobalt Plateaus.

Astrotrain drops off a character at the start of an event and then picks them up at the end. Astrotrain follows behind out of sight, ready to drop off and recall buddies, and brings him/her back if he/she happens to fail.

The interior of Astrotrain is essentially the base of operations and barracks for the Autobirds or Deceptihogs, as upgrading, recharging, customizing the characters, and claiming Mission prizes all takes place inside Astrotrain.