Darvin: Haven't had a chance to try multiplayer yet (the handful of times I've looked it's been empty, or in one case had a private game) but here are my experiences vs AI:

- The AI is very quick to drop all its monsters and all its mana in lightning bolts on top of your head; don't fight on its territory unless you know you have a decisive advantage.
- In the same notion, the AI is very quick to commit everything to a single battle, meaning that if you can lure it into a line of traps you can utterly devastate it. You can then repeatedly lure its (very thinned out and low level) forces to prevent it from ever building up to a significant threat again.
- I've taken to leading with Beast Den / Prophecy / Annex with my three starting sins. Workers are really bad at leaving unclaimed tiles right in the middle of a room, and having Annex at the start of the game lets you fix that without having to divert them away from other tasks (also lets you speed up a bee-line to something important on the map)
- Putting a treasury near any gold you're harvesting vastly speeds up how quickly your workers can mine it. It is very annoying to pick up the gold and move it to a more secure, location, however.
- If you capture an enemy stone bridge that contacts a stone bridge on which you've built traps, you should immediately sell that bridge, as if the enemy recaptures it they will take your bridge as well and the traps will be destroyed. Putting a different kind of bridge in front of your stone bridge can be used to safeguard against this.
- Always be sure to warband any minions you care about before dropping them near enemy territory, as they can easily pursue enemies over the territorial boundary and then get smacked down instantly by a barrage of lightning. You also can't pick them up in enemy territory, nor can you recall them if there's so much as a level 1 oculus attacking them. Keeping them tied to a rally flag keeps them safely in your territory.
- If there are heroes about, make sure to get a torture chamber / prison combo operational as soon as possible, as heroes are often found at very high levels and can thus add an enormous amount of combat power to your fighting force (especially true in the final level of the campaign, where my offensive force was mostly converted heroes at the end since there were so many high-level ones to convert. I had a team of peace-banded succubi on full-time "recruiting" duty).