Note: This is the 2007 game by Codemasters, not to be confused with the 1990 Overlord game by Virgin Mastertronic.
Forge a piece of gear without imbuing anything into it. Then, upgrade it and put as many minions into it as desired. As soon as the animation starts, but before any minions jump into the smelter, pause the game, save, and exit. When you return, the minions will have been imbued, but will not have been taken from your supply.
To do this trick, you must first have fought Dazzler Beetles (found in the blue minion cave), Puff Beetles (Evernight), Magma Beetles (outside of Heavens Peak), and Battler Beetles. After you have fought at least one of each, they will be available at your dungeon. Go to your dungeon and choose to fight one of the four. The easiest way to take out the horde of beetles is to pull only a few from the swarm and take your time killing them individually. Green minions work well due to the fact that they are experts at overwhelming and killing your enemies. Set a marker for them to wait at and they will eventually turn invisible. Pull a few beetles and make them follow you to the marker, where your minions will then jump on them and eventually kill them. Battler Beetles are good for getting Brown souls. Puff Beetles are good for getting Green souls. Magma Beetles give red souls, and Dazzler beetles give blue souls. You should get at least 75 souls each time you completely kill all of the beetles that are in the dungeon.
Use the following trick for fast green minion soul gathering. When you find the green minion hive, you will see five green minions jump into the spawning pit for you to take control of. Do not do that; instead, go to the tower using the gate beside the tree spawn pits to your right, then return to the green minion hive. Five more green minions will jump into the spawn pit, and you will still have the ones from before. You can do this as many times as desired, but after you take the hive it will no longer work.
Always have blue minions on guard duty. While on a guard post, they will actively run into the combat, grab a fallen peer, and drag their half conscious form over to you so they can revive their fallen comrade. However, while not assigned, they will wait for you to micromanage them over to the body by sweeping, making them almost useless in a large battle.
When there is water in front of you or blocking your path, only you can walk through it. If your goblin minions go out of the shallow end of the water, they will drown, and can only be saved by blue goblins. Instead of guiding your goblin minions across a complex path to keep them out of the water (which they usually fall in anyway and drown), just walk through the water. Your minions are smart enough not to follow you and will automatically seek the easiest path to get back to you. Be careful; sometimes your minions cannot get through because a bridge needs to be activated (for example, Blue Goblin Cave).
Target-lock onto Rollie, and start to circle him while he prepares attacks. After he attacks, you should be able to get directly behind him while he pauses and circle up to his side. Stand against the tank treads on his side, and start hacking away at him. He will not move or try to attack you. You can defeat him in each phase of the battle this way, and it requires no minions.