[Endoperez]

+Penetration items would be Eye of the Void (astral), Spell Focus (astral) and Rune Smasher (Water/Fire).

There are also some items and spells that work especially well against demons. The manual list of spells is a good place to start from. Look for low-level Astral and Water spells that deal extra damage against undead and/or demons.

Also, don't worry if you lose. Learning how to beat difficult opponents is part of the fun. You can try again with the same nations, or choose a different nation against Yomi, or play AS Yomi to see what causes you most trouble.