Atlas

Question : What happens if a Gigantic Character is played during the tiebreaker?

Answer : Its statistics are counted twice: once for the Hero Expedition, once for the Companion Expedition.

Question : If a Character is both Gigantic and Defender, for example because I control both Atlas (Rare, Ordis version) and Gulrang & Tocsin, what happens?

Answer : "My Expedition", for a Gigantic Character, means "my Expeditions", plural.
Therefore a Defender, Gigantic Character would prevent both of its Expeditions from moving forward.