How do I get "The Good Stuff"?

The achievement description says,

Win a match by collecting only mithril

Even with the highest mineral setting, getting down deep enough and being lucky enough to have several mithril deposits is uncommon enough and, even with the lowest AI settings, that doesn't seem to be enough to beat them.

I've tried using a monster swarm with the highest spawn setting to keep the enemy out of commission, but the ramp up until the other team is overrun is long enough for them to score better than all the available mithril and, if the map runs long enough, I get swarmed too.

I'm surely missing something.

Monsters drop minerals in mixed batches so that would invalidate the "only mithril" aspect, wouldn't it?

Can I collect relics and still get the achievement?

What's the trick? What's a simple strategy to get this or is it simply a matter of luck and the AI getting terrible relics?

After repeated attempts, this proved to be something not likely doable when facing AI opponents alone. It turns out that some achievements can be earned in local multiplayer and, thankfully, this is one of them.

A simple strategy to win this achievement is as follows:

• Set Monsters to the lowest amount to avoid interruptions.
• Optionally set Minerals to the highest volume to make mythril easier to find.
• Optionally set Relics and enemy AI to the lowest values to make it less likely that an AI opponent will score from Relics or will obstruct you.
• Play a map with easy access to the Deep level, such as Cliffs of Blandness, picking the lower starting point. A two-player map will be the quickest because there are fewer players that need to take turns.
• You can try lowering the number of turns to make it a bit easier, but the default should be fine if you are in control.
• Set two or more of the teams yourself to begin the match in hotseat local multiplayer where you are controlling that many teams. It's not as much about quantity as movement in this case so having one or more Scouts will make this easier to avoid mining the wrong mineral.
• However you go about it, be it controlling all teams or facing some AI, prevent the other teams from scoring much if at all and have at least one unit on one of your teams collect only mythril, making sure not to pick up or turn anything else in. Be careful of mining the wrong minerals, especially where the game obstructs the display of the mineral type.
• Once you've turned in enough mythril to score more than the other teams, you can pretty much coast your way to this achievement.

I did not have the opportunity to test whether turning in relics invalidates this achievement because I simply made sure not to pick any up. I am confident that monster looted minerals that are not mythril will count against this achievement.