Age of Wonders: Planetfall

If you've already finished the campaign, look to Hazar's solution. If you haven't completed the campaign and want to pick this up while you are it, read on for my suggestion.

There are number of units, mods, and tactical abilities that allow you to take permanent control of enemy units. My recommendation is to use Psi-fish Siren units. You can get these units as a rewards for faction tasks, or you can trade for them once you have a high enough relationship. Once they are in your army, target an enemy force with bi-ped organic enemies, and engage in manual combat. Use their ensnare to draw an enemy bi-ped unit to point-blank, then use the impregnate ability on the following turn. I don't remember a single time the impregnate ability was unsuccessful. Two turns later the enemy unit will die when the eggs spawn leaving a chrysalis under your control.

Buying the mod to increase the Siren's ability range and outfitting them with it helps as well.
And make sure you don't kill the units you are targeting with the Sirens with another unit's overwatch, melee or ranged. They'll run up the Siren once ensnared and then run away once impregnated.

You can save before a battle to farm this if you want, if you take 6 Sirens in and have sufficient targets you'll have it after only 5 repeats. But I found this tactic worked well to pull out victory when at a slight statistical advantage forced manual combat rather than auto-combat. Of course if you don't have the achievement for 100 wins in manual combat then you can work on these concurrently.

The syndicate subjugator unit can also mind-control units, though their range is lower than the Siren's ensnare, getting the unit rather than a chrysalis might be worth the trouble.

I also suspect the Condemned to Drain tactical ability for Heritor commanders works as well, so the last mission of the Revelations campaign would also be a good place to work on this achievement, though I had already unlocked it so cannot confirm. Creating Drained units though does make collecting 500 Essence Charges a lot easier, so another opportunity for synergy.

Zero reason to have a ratio like this ;)

Setup : Skirmish
Small frontier world
2 players, both amazon
Any setup (promethean or bio, any hero background) you like, I recommend bio super.

As you start:
*Research protective grounding (t1) from military
*Research Frontier Facilities (t1) from society
*Explore, but leave G/R mantis, B/R crystal rock beasts, and any other *animal* trait (as opposed to cyborg or mechanical trait) npc alone.

Explore a bit, begin military structures for defense or colony pods, then as research opens;
*Research Primal Control (t3) from military
This unlocks Primal override this (80 energy, 4 tactical power)
*Research Area surveillance (1)from society
*Research Operation Effectiveness 1 (t2) from society directly after.
Each OE from society gives you +2 tactical combat op points
Doing so lets you work on the achievement as they finish

Going into MANUAL combat, the operation Primal Override gives you a chance to mind control animals. If they *Survive the combat*, you keep them, with the cheevo going up by 1.
(This means saving before a battle lets you farm take overs. With 12 tac points and 240 energy I got this in 30 min)

So,
You may now either pool energy and research more operation effectiveness from society, letting you cast the operation multiple times in a combat, or go combat to combat getting what you can.

*The ai amazon never attacked me
*Growth npc faction has bee units you can control
*Dont forget to keep your colonies happy, defense structures help as your armies cant be everywhere.

I'll answer any and all questions
Happy hunting (>*_*)>

Age of Wonders: Planetfall (PC) - Achievement - Wololo

Permanently convert 30 units to your side

A simple enough method for this achievement is to use Psi-Fish Sirens purchased from their dwellings once you enter 'Friendship' state with them on any particular map. 'Eyes of Eternity' is a good MOD to use with them as this increases their range by 2 hexes.
Use their 'Enticing Bond' ability to draw a unit in close against its will and then use the 'Impregnate' ability when the enemy unit is next to your Siren. This results in them fleeing for 2 turns afterwards and then dying, resulting in a Psi-Fish Chrysalis spawning in it's place under your command. This counts towards converting a unit.
The first Kir'Ko campaign level in the Planetfall base game is your earliest opportunity to do this method if you're playing the campaign as Psi-Fish are present and you have the option to fight Vanguard troops. Please note, this can only be used against humanoid biped targets.