I recommend a Slann with Focus of Mystery. You can use Walk Between Worlds to give units ethereal for an out of phase move. When they are ethereal they can walk through Goblin Fanatics with no damage. In addition you can peg the Black Orc leader (I'm guessing it's Grimgor Ironhide) with Arcane Unforging. You take away his magic items and he's a lot less scary.
For a non-magical solution, skirmishers are a decent anti-Fanatic tool. Typically, if you trigger three Fanatics, one will self destruct, one will go down to Skink shooting, and the third will hit the Skirmishers. For more detailed anti Fanatic strategies, give
this a look.
You probably want to use Contemplations to swap out spells, you want to take Metal and pick up Searing Doom (the signature spell) to soften up the Black Orc block as a whole (though Searing Doom won't help against non Black Orcs).
A lone Slann with Higher State of Consciouness can kill Fanatics with impunity by floating into them. If you keep him away from the big blocks, he's pretty safe. Doom Divers and other O&G artillery can't hurt ethereals at all.
I don't know what your whole tabletop situation looks like, but I'm guessing that two Saurus blocks of 30 will outperform 3 blocks of 20. That gives you staying power and maneuverability.
If you opponent uses a lot of rock lobbers, Ancient Stegadons would be a liability. But if there is relatively little hard hitting artillery, Ancient Steggies would be great for one-two punches alongside Saurus Warriors blocks.
Check out the general
Orc and Goblin tactica if you haven't already done so.