Too Human

Trolls are present in every level of the story, they're not rare enemies but you won't come across them constantly so it's a good idea to try and mount kill every troll you come across until you have this achievement.

To mount kill a troll you must first destroy it's chest armour, this is the absolute minimum, I often destroy it's weapon too, just to make life a bit easier, from here there's one of two ways to do this depending on if you're playing solo or if you're playing co-op.

• Solo;
It's harder to get a mount kill in solo play but is by no means impossible, destroy the Trolls chest armour and his weapon, once you've done so move in toward the Troll. When you feel you're close enough use "B" to roll around him, it might take a few rolls but when you're behind him the "A" prompt will appear in the top corner of the screen, from there use the "LS" to keep your balance on the troll and then when you're levelled out use "RS" to swing down your melee weapon.

• Co-op;
In co-op not only can you use the above method, you can also have your partner distract the Troll while you sneak up on him and initiate the mount kill.

Something important to note, if you're playing co-op and your partner gets a mount kill it will add toward your total too. It seems that in online co-op modes all kills made between players count toward each others total as well as their own.

First, aim at the Troll's hammer to destroy it. Then target and destroy their chest armour. Now get behind it and hop on. It will try to throw you, just keep your balance. When you are mostly balanced hit attack to finish the Troll. Repeat 49 times.