Native Mercenary idea:
Osage Giants - A robust archer with a fast rate of fire.
The Osage people are notable for having explorers note upon their unusual height as well as the wood of the osage orange tree being one of the best woods on the prairie for a bowyer - I know even my own uncle has referenced this.
With this, an unusually tall archer with more health than usual and a fast rate of fire would make for an interesting Age 3 Mercenary unit, and potentially be an infinite card shipment for the Lakota, as the Osage are also a Siouan people and would have been within the sphere of influence of the Oceti Sakowin (the Seven Fires).