Stags, also known as Deer, are the largest species of deer in Narnia.
The Magician's Nephew
Stags were among the animals that were called out of the ground by Aslan. They were among the queerest looking animals as their antlers were sticking out from the ground long before they came out, looking like small trees.
The Lion, The Witch, and The Wardrobe
In LWW, a White stag was been chased by the kings and queens in the forest of lantern waste.
Prince Caspian
In Prince Caspian, the stags are seen with the old Narnians ready to fight Miraz.