Just the TipG 15

I managed to get this one during the 4th campaign mission, "What is this s#*%?" During this mission, you'll be stuck waiting for an elevator and a blood dragon will come rushing down the hallway at you. Before it get to you, run over to the nearby vending machine and equip the minigun, the Fazertron, the bow (duh) and some C400 if you feel so inclined. Make sure to stock up on ammo too.

Then just let the dragon chase you in circles around the crates in the middle of the room while you get its health down real low. I used the minigun to do most of the damage, although I used 500+ rounds in doing so, you might want to use some C400 to do some of the initial damage. Then to be safe, I used short bursts of the Fazertron to get the health down to a sliver. Be careful here, it's really easy to kill it prematurely. Then just keep plugging away with arrows, preferably in the glowing underbelly.

After getting the health down to a nearly invisible bar, it still took about 10 arrows to put 'er down. So if you've left much more than that, you may have to resupply arrows.

This achievement may seem a little frustrating but I really isn't that bad depending on what method you use to take on the Blood Dragon. Doing it out in the open will be harder of course since it will be harder to avoid. The best method for taking on the BD is to find one near a Garrison you have liberated and lure. It right outside the barrier, it won't be able to enter. You can start this achievement early on anytime after you've liberated your first Garrison which is where I unlocked it. Along with the having the barrier, another good reason why working towards this achievement at a Garrison is because you'll have access to the weapon/ammo vendor in case you run out of ammo. You'll definitely want to be fully stocked with grenades, C400, and shotgun ammo. I was able to use just those weapons, and the rifle a little but it does very little damage. Continue shooting and throwing them at the dragon until his health is practically run out, pull out your bow and make the final kill. His stomach is the best area to hit and will cause the most damage but if It's health is low enough you can kill it with a head body shot. Make sure you Dodge the laser it shoots, using cover from the walls of the Garrison will help like I did, because if you are directly hit even once you'll be killed. If you wait to try working towards this achievement until after you've completed the first main mission you'll have access to the Terror 4000 which is a great weapon to use against dragons and will lower their health a lot faster. Here's a video I posted from when I unlocked the achievement. (Also unlocked "Blood Dragon Down" since it was the first dragon I killed. Start watching at 0:56 because that first minute is when I unlocked the "Running man" Achievement.