Shamans are Eagle Tribe support units on Iki Island who stay at the back and chant to power up nearby Mongols. Buffed soldiers get double health and turn far more aggressive, so the shaman is your first target.
They keep a safe distance and sing, while the troops around them get tougher and wilder. On their own they are weak, with only a staff to swing.
Kill the shaman before engaging the rest. An arrow from cover or a quick rush works, since they can't hold you off. A Standoff won't pull them in, so you need to go to them.
Eagle Tribe
The Eagle Tribe is the Mongol force that has taken Iki Island, led by the shaman Ankhsar Khatun, called the Eagle. They are the main enemy of the Iki Island expansion, and their purple-uniformed troops bring units you never see on Tsushima.
Switchers
Switchers are purple-tier Eagle Tribe soldiers on Iki Island who carry several weapons and swap between them mid-fight. You have to keep changing stance to match whatever they are holding.