I'm really not a fan of <fill-in-the-blank> is OP'ed threads so I'll say it this way instead... I'm abusing the AI with Pull of the Earth.  The AI has become much better and puts up a really good fight until I get Pull of the Earth.  The problem with Pull of the Earth is that all your heroes get it regardless of what class or magic school they are.  So I take an army of 3 heroes plus a bunch of troops (pick any 6) and lay everybody down with Pull of the Earth and then just poke them to death.  Here are some ways to fix this:

1) Switch Earthquake and Pull of the Earth.  Earthquake is more like Curgen's Volcano anyway (a once a game type spell) and make Pull of the Earth a Earth IV or V spell.  That limits its awesomeness to only heroes with Earth IV or V.

2) Add a 1 turn costing cost.  I hate casting costs.

3) Un-nerf your Horse and Warg overnerf so that the AI can build more prone-immune units

4) Encourage the AI to build more units wearing prone-immune spider boots