'Eternatas' was wrongly translated from Affleck. Actual name is 'Eternabbas' and is a tiny and bizarre looking bipedal Bug/Dragon pokemon with w disproportionately large and triangular head in contrast to its body. I'm not talking Turner's usual fetish with bobble-headed pokemon. Think Pyramid head with tiny teeth and Venomoth eyes.

Eternabbas is, predictably, the source of the Dyna and Gigantamax phenomenon and it has its own Gigantamax form. It looks very much like a gigantic insectoid and bipedal Porygon. It's extremely angular and its body consists of a single triangular segment that looks somewhat like a rigid "dress" with Dynamax clouds eminating out of the bottom.

Eternabbas serves as the primary antagonist and the final battle in the main campaign is against it's Gigantamax form in a raid battle with NPCs (Leon, Hop, Marnie and yourself).

The fight is mostly scripted, and you are locked into using your box legendary. Unlike other raid battles,all four of you take turns Gigantamaxing your Pokemon and Eternabbas OHKOs them in turn- Marnie's Weavile, Hop's starter, then Leon's Charizard which leaves you as the sole fighter against it. Again, it's mostly scripted up until you're the last one standing which is when the "real battle" begins, so to speak.

After defeating Eternabbas, the Dyna/Gigantamax phenomenon ceases to exist until you do a postgame sidequest to capture it in its tiny base form, which will allow you to rechallenge the Gyms and League in a "Master League" which increases their difficulty and Pokemon roster.