The #1 thing that needs to be in TLC 3. At least make it as large and powerful as the mosa. Should have one of the highest attack dammages because scientists have proven that the megalodon has the most powerful bite of any living thing and is strong enough to crush a tractor trailer.
Wild mantas can be fairly hard to hit with a megalodon.Just keep your shark still and the manta will often swim in front of its head.the rest is easy enough.with a high level megalodon even 120 mantas only take a few hits
You can’t eat or drink underwater which makes healing or renewing your Fria Curry or Lazarus Chowder a problem - Megalodons can swim straight up and straight down unlike some other aquatic mounts and when surfaced, you can dismount and stand on them to eat or use healing tonics. With enough HP you can set them to passive and let them tank damage from a Megalodon while using your rifle to dart the wild megalodon for a faster KO. Always best to have a few sharks with you while exploring the oceans.
Getting one megladon makes getting more a lot easier. For what ever reason it aggros wild ones quite far. Just swim underwater and spy class the one you want. Lead it to the coast and begin tanqing. As for underwater usage. My 225 6k health and 364 melee was able to take an alpha megladon solo. I did manage to kill a lvl 70 alpha but needes help from rexes. Fairly good underwater would recommend 2 or more for higher level alphas though.
A very useful early ocean going mount. Be sure to set it to passive so it doesn't swim off to where you can never find it again. Also level up on your oxygen so you won't have to make it surface so you can breathe all the time. Quite possibly a good ocean beasty tamer. Mine swam off killing things and I never saw it again. Emphasis on setting it to passive.