I've looked up videos on taming these guys but none really seemed helpful because I'm on PVE official server. But I managed to tame these guys easily by going in the cave with a carno during day and clearing it out until mega is left. Then lure it to the water and trank it. And for some reason they don't seem to lose oxygen while under water.(as of may 20th) And even when it wakes up automatically at night it still swims very slow.

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