Well, at last I did find a way through lv3 inferno heroic, and suprisingly it was very easy. So time to share
1.choose PF as bonus. Fight gate without PF and succubi losses, you may take them out of battle if its necessary.
2.Capture southern town asap. then saw mil, gold mine to the left, gem mine. I pass the mines with mages and priest.
3.Try hard to fight neutral monster, if there is PF or succubi losses, load and play again. Dont up Inferno town, only town hall and market, you may need horned demon for archers block, too.
4.end of week 3, i have all sylvan dwelling, but no upgraded one, and did pass through the red gate to collect mercuries, and capture crystal mine. The sulfur and gold mine guarded by priest still not (i didnt want to lose all my creatures)
Till now there is nothing special. I had a hard time fighting neutral monster that the druids creat, many losses. End of week 4, gileran (or wtv his name is) with an army 2 times as mine come to me. His army is all upgraded, 6 emerald dragons, I had 3 greens. I tried to fight him 2 time, all lose. Then I run, direct to where I saw him appeared. And OMFG, he did capture all my mines, but not the town !!
Some bugs, definitely. I comfortably take the north east town (guarded by 100 pixies) with full build, upgrade my army and ... wait. After 2-3 weeks his army is nothing compared with mine (6-12 dragon) and I almost want to hit the auto combat button
I never fought phoenix, or dragon etc. Gileran does it all for me )