This thread is nearly 2 years old. Does it mean that Yomi is in for an imminent upgrade?
I really like KO's idea of reducing costs and having the ghosts flee the battlefield. Not only would this fit the description of "near immortal" better, but it would allow players to try and come up with innovative strategies and make Yomi play very differently than other nations. I think this would add a new twist to EA Dom as other players would need to adjust when playing Yomi.
The cost reduction would still need to be substantial though. FWIW I could think of interesting possibilities if they are reduced to the following:
Ko-oni: 6 gold and the summoned version (MA) would be 10 for 5 gems.
Ao-oni: 16 gold
Aka-oni: 20 gold
Oni: 30 gold
Kuro-oni: 40 gold
At these prices they might be too hot for the AI to handle, but a human player will adjust and concentrate on banishing them rather than engaging in a fair fight.