Panharmonicon
Underhanded Designs

If I have an Underhanded Designs on the battlefield and then cast Panharmonicon, will the Panharmonicon's entrance to the battlefield cause the Designs to trigger once, or twice?

I'm 82% sure that it causes the Designs to trigger twice, on account of the Panharmonicon doesn't say "another artifact or creature" and because in order for the trigger to be put on the stack the Panharmonicon has to be on the battlefield (having freshly entered it). Therefore the Panharmonicon's ability exists at the time the Designs's ability triggers, allowing it to trigger a second time. Please correct me if I'm wrong.

It triggers twice. There are some triggered abilities (primarily leaves-the-battlefield ones) that trigger based on the game state before the event happens, but that's not the case here. It triggers based on the game state after the event happens, and at that time, Panharmonicon is there to double the trigger.

Ok, thanks. I had to give a ruling at the local prerelease yesterday about it and wanted to make sure I gave the right one.