I figured out the easiest way to tame them! You'll need a Deinosuchus since they barely get knocked back from the Acro due to their low stance.

Ride the Deino and bite the Acro until the Acro does it's feeding roar, then dismount quickly and feed the biotoxin. Get back on the Deino and repeat. You'll be tanking the Acro's attacks so watch your Deino's health. When the Acro does its stomp or fake roar, stay on the Deino and you'll only get knocked back a tiny amount. You can easily knock a max one out in a couple of minutes this way.

Since nobody gave a good tutorial on how to tame this beautiful beastie, here ya go:

What you need to bring:

Mastercraft Shotgun or Sniper Rifle

Lotta rounds for the gun

At least 30 Bio Toxin

50 Exceptional Kibble(just in case)

Acro Saddle(for after it’s tamed)

A flyer or really fast mount that you can wield the gun from

Anyway here’s how to tame this beautiful creature:

Firstly, find an Acro, then once you find one that you deem worthy of joining your army start shooting it on your mount’s back from a close-ish range, after it enters shield stance unload on it until you get the right roar, two roars exist. The fake roar is way less dramatic than the actual one, which you can tell apart because the real one, the Acro will raise itself up and roar at you, and there’s also an effect around it. When it does the real roar, dismount your creature and run up to its mouth (terrifying, I know), and mash E or whatever a console players interact key is. If you miss the feed, it’ll enter adrenaline mode and you gotta RUN FOR YOUR LIFE, after about 35 seconds, the adrenaline is over, so get back to shooting the Acro’s poor face.

Rinse and repeat this process (preferably getting the Bio Toxin in its mouth), and once this glorious beast finally goes down, yeet that kibble into its inventory and give it a bit (put whatever Bio Toxin you have left in there too just in case), after a few minutes or so, the Acro wakes up and is ready to be your war mount!

When taming these dont try to trap them as it typically causes them to never go into shield stance. Fret not i have an easy guide, once you get it into shield stance count how many shots it takes to enrage it (normally 5 with a good pump) shoot your amount of counted shots then back up and it will roar, then run up and feed it your narcotic or more ideally biotoxin then immediately back up a good distance and as soon as it is done with its animation it SHOULD go right back into shield stance allowing you to rinse and repeat this method safely on foot. WORDS OF WARNING kill everything nearby as to not mess with the process, you know you are safe to start shooting when it stands straight then goes into its shield stance, ONLY approach it AFTER it does the correct roar since it has 2 roars, the one you are looking for and a fake/taunting roar which if approached when its doing this second roar will cause it to enrage and and start attacking everything for 30 seconds and will kill you very quickly. IF it does the fake roar simply stand back a good bit and wait for it to finish, after it does it'll do the correct roar and you then run up and feed it like normal. with this method and a little practice you can tame one without ever really getting hit whilst on foot. ALSO the second roar isnt nearly as loud as the first and looks a bit different and the acro will laugh at you (literally) after doing this fake roar if it doesnt get enraged by tricking you. Lastly these things are BEASTS, you and a tribemate can grab 2 bred acros with asc saddles and kill alpha monkey with just those 2 acros, they can also solo the hard ice cave on the island but youll want a good saddle, hope this helps and like so others may see

Mount a turtle. Shoot from turtle. Thank me later.

be VERY careful of their bluff roar, but if it gets triggered, i found that if you deal enough damage (i used a 220% pump action shotgun on a level 140, and three point blank shots to the face) while its roaring, it pretty consistently does the roar that lets you feed it right after. it doesn't always happen, so don't get too eager and keep some distance or stay to the side so the knockback roar doesn't happen instead.

You can’t tranq this Dino you must shoot it until it roars then run up to its lower jaw and feed it biotoxin. My buddy try to tranq it and used 88 of our tranqs. Enjoy this info like we would’ve

I highly recommend using a Deinosuchus as mount.

Highlevel Acros will deal you quite some damage which makes it super nerve wrecking & unnecessarily difficult to tame them on foot, especially when they knock you back - which the Deino is immune to: making it easier to force-feed them the toxin in time!

You don't need to target its mouth when feeding narcotics or biotoxin, any part of its body will give you the option to feed.

A bit confusing, but a good way to tell a wild acros damage stat without mods:

Use your own acro. Get into shield stance, and force wild acro into shield stance. Whatever the damage done by the acros BITE in shield stance to your own acro in shield stance is the damage stat. For example, if it does 33 damage per bite, it has 33 points into melee. Nothing game breaking but I thought I’d share