The astrotecus is a ez tame all you do is get a meck give it large gun then go to space ship and shoot the floating humming whale and avoid the void wyverns and small whales and you fine.
When I was in the ocean near the mountain I saw one grab my bary and it was being eaten alive and I saw it say feed to tame so I tried to feed it but my bary already died and I think the reason I was able to tame it…