To get high efficiency you need to let it eat a lot of blood.

Prepare a few hundred blood packs get a tame they can grab like mochops put the blood packs into its inventory and lead the desmodus to it. They will grab it and then let it fall down and fly around for a bit u till they grab it again. This will take a while every time it grabs it the taming efficiency will rise by a few percent. Sometimes the desmodus will fly to far and not go back then you need to guide it back to the mochops. Once taming efficiency is at 100% you need to let it grab you to finish the taming. For this it's good to have blood packs in your inventory and maybe a parachute as they will let you fall down once they are tamed.

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