Perpetual Motion Device
Perpetual Motion Device is a Riggs artifact that lets you draw 1 whenever your hand is empty.
Strategy
This artifact can be hard to use, as most decks aren't able to play every card they draw due to Energy constraints, and that means this won't do anything most turns. It also has awkward anti-synergy with Riggs's card draw effects, which make it even harder to reach an empty hand. In many runs this artifact won't do anything.
With that said, Riggs does have plenty of 0-cost cards in her pool and upgrades to 0 cost. Basics can also be upgraded to 0 cost, and CAT and Books also have 0-cost cards and synergies with them. The more you build into this artifact, the more it does for you, and each successive investment is more powerful than the last.
Note that if you can get your deck to a point where all cards are 0 cost, you can just keep playing cards over and over again infinitely, and with the right cards this means the fight (and possibly the run too) is already decided in your favor.