[Boron]

Elemental magics are dangerous because a doom horror has 2 misc slots so he has probably 2 of the 3 items : Amulet of antimagic , Fire/Lightning resistence ring .

In own dominion demilichs just scripted to drain life are a very good counter .
If you want to go with elemental magic i would suggest trying frozen heart because the doom horror likely has no cold resistence .

A doom horror is a magic being so you could try a few high attack thugs with moonblades , devils would be excellent there because of 18 base attack value and cheapness . Just add a ring of the warrior + a burning pearl for +9 attack and you have a good hitting chance .

Your devils won't survive more then 2 hits by a doom horror but they don't need many more against him neither .
One such devil thug costs only 30 blood + ( 5 fire + 5 astral + 5 Blood + optional 10 water or 5 water / 5 earth for a quickness item ) x forge boni vs. 100 S + 20 N + 2 misc items .

Btw : Imo the 2 best wishes are for gems and for blood .