for this achievement you have to go to the bottom right of the screen and click on fights
i suggest working towards vsing people with bounties on them first because you have to get 500 wins against them and kill 500 air and land units work them together.
i can confirm that you can send one lot of troops out start it and then the top right of the screen click retreat it counts as a match you're troops lose a bit of health but rinse and repeat seems to be the fastest way i figured out.
Win against all the easy enemies and lose against the hard ones it will keep your level down in vsing people (those things under your avatar picture level) it will help you find easy bounties more so you could be level 30 vsing level 15 and have better units to smash them
shouldn't be able to down vote without giving a solid reason why