Question

Can I get Arceus from gts negotiations or do I need to get it from events?

Answer 1

Both.

You can Trade for one OR wait for another event.

Answer 2

Three ways to get Arceus:
- 1: Trade with someone;
- 2: Wait for an event;
- 3: Obtain an Azure Flute (Key Item) in a DPPt file. However, this is an Event Item that hasn't been made available (yet), but at least you could trigger a fight with a Lv.80 Arceus and attempt to catch it, thereby stamping your Trainer ID number onto it forever.