Minion Masters

You can get this quickly by spending real money, but it's not necessary. As you are going for the other achievements, you will earn a lot of gold and rubies. Just spend these two resources on nothing but Power Tokens and you will eventually get this achievement.

Each Power Token costs 1000 gold. You can also buy two Power Tokens for 160 rubies, or ten for 725 rubies. You'll get most of your gold through daily quests, Battle Pass tiers, and gaining new ranks. You can earn rubies randomly by spinning the free daily tokens.

You can also often get a small amount of gold for free in the shop. Just check it daily and see if the free gold is offered. There are sometimes free shards offered as well. The gold you earn from battles is minimal, even if you win, but it adds up.

It goes without saying, but make sure you actually spin your Power Tokens for them to count towards this achievement. This game thankfully has achievement tracking, so it's easy to monitor your progress.

Thanks to Lockie for the following info: Season Tokens convert to Power Tokens after the season ends, so you're better off not opening them until they convert.