Edit: Sounds like the limit is 2 energy per opponent per combat, except in the case of first and double strike, which triggers Pia both damage steps. Thanks Lemmy!
Edit 2: Here's the deck if anyone's interested!
Original question:
I'm a bit confused on her first ability. If 3 artifact creatures did combat damage to a player, would that make 6 energy, or just 2?
It's the "one or more" text that makes me wonder if there is a cap of 2 energy per combat. Hoping not since I want to make an energy commander deck with her.
Any number of artifact creatures dealing combat damage to a player will generate a total of 2 energy. You're right that the "one or more" text puts a cap on it.
However -- say you have three artifact creatures, and one of them has first strike, but the other two don't. When the first-striker deals combat damage to the opponent, Pia's ability will trigger, and you'll get two energy. Then when the non-first-strikers deal combat damage to the opponent, her ability will trigger again, and you'll get two more energy.
Another way to get more than 2 energy out of her in a turn is to use "additional combat" effects.
Thanks! I'll look into a first/double strike sub-theme, and additional combat as well
Depending on your format, some of these could help you get some additional triggers too.
https://gatherer.wizards.com/Pages/Search/Default.aspx?text=+%5B%22additional%22%5D+%5B%22combat%22%5D+%5B%22phase%22%5D&special=true