If you are planning on doing anything involving water prepare to despise these flat horrors. They can out swim you. They can swarm you. They can act friendly and once you turn your back eat your tame. Beware.
When I was still a noob and didn’t know anything I saw 3 mantas, I didn’t know if they were aggressive so I went to check if they were at first for some unknown reason it didn’t attack me they just acted like ichthyosauruses so I thought they were passive but then when I tamed a low level ichthyosaurus the mantas started killing my ichthyosaurus I was like WHAT I THOUGHT U GUYS WERE SUPPOSED TO BE PASSIVE then it killed my ichthyosaurus, i went to check again but this time they killed me R.I.P me and my ichthyosaurus
I was swimming back to base on my sarco and when I get back to base I turn it off I come back to find my sarco missing but not dead me 17 days later: let’s explore the ocean on our Meg next thing I see is a sarco swimming in the ocean killing mantas fortunately I brought sarco back to base and tail stunned them with my baryonyx
If caught in open water by a manta fight don't flee. If you have a spear or pike swim up as it gets close. This keeps you above it attack area and puts you in striking range. The manta is slower moving up and down in the water.