Best to bola them near the shore of the arctic region. Keep pumping narcotic into them as you can run to your boat with warm campfires and then run back. Wait a bit recover health, stamina hunger, etc, then go back to the megaloceros.
Easy tame, just use bolas, trap/protect it with spike walls, feed berries, and use narcotics/narco berries to keep torpor up. I play on a small tribes server and tamed a max level in less than an hour with 3x.