Windows 8 and Phone: Loading up your cloud data to replace your local save will reset your killcount. Anyone going for this achievement on both systems (OS) will need to repeat this.
You will get this achievement as progress through the story line and missions.
Note: All animals are included in this count - sheep, cougar buffalo, etc. - I can confirm this myself as I unlocked "Natural Born Killer" after killing a sheep.
It is best for you to reach level 35 and accumulate 500k for the Gatling Annihilator. This weapon is extremely OP even at tier 1-2 upgrade . In the long run you will save hours of gameplay. Going through the levels with any other weapons such as (longshot repeater, dual guns, shotgun, telsa, Impaler, etc). are nothing to compare. Do not bother will full upgrades. Its best to save yours stars for auto-complete for Jama-Jama Mission round 45-50. (30 stars)Note: You can play the lottery many times by changing your PC date, however, getting those stars are rare.
Please refer to the farming method for Demon Hunter IV.