The soul stone allows you to cast call of the wild once a turn for free. In combat it gives you a bunch of wolves each turn.
According to the spellmod, tha hama dryad has weapon id 284, which is steal strength. Yeah, they suck.
The usual tactics against ghost riders I've seen/used include equipping a high penetration mage casting a spell that targets the wraith lords (like Charm) as the riders will dissolve if the leaders die, getting a bunch of priests casting banishment with some high protection troops to shield them, fielding SCs that can off the riders without too much trouble. (Luck and etherealness and prot of 20+, preferably combined with fireshield, in the way of an example.) Another option, especially with stealthy armies, is to sneak every other turn, which prevents the Ghost Riders from ever catching them. Then use said army to take back the ridered provinces; in theory two such groups can keep a province from enemy hands. (Attack the province on alternating turns.) Anything that can off a scout/spy is enough, so maybe army is a bit strong a word.
In this case it's probably a waste of time to try to target the casters, as they are likely lamia queens or wraith lords or demiliches; the latter are immortal and the lamias are pretty buff. Also, a prudent ghost riderer twiceborns any living mage to prevent any mishaps, especially with the increased level-demand of the mod.
Castling will also reduce the damage done; it's not an option for you with your huge castle, though
You should really try a game sometime with a 40 admin castle: It costs 300g and 2 turns less to build and offers almost the same level of resources and gold and supplies.
There's little you can do to prevent/survive a ganking, aside from aggressive diplomacy. It really doesn't matter who you play against or how: it's always preferable to attack an opponent with superior force, so weaker opponents will band up to gain an advantage. If you are the strongest there is, there's no single nation left with enough force to challenge you alone; thus you'll be ganged on, unless you can do the diplomacy to prevent it. Ask Chris how he does it: it looks like he's first convinced Aku that I am the greatest threat, and now he's convinced Boron of the same thing, while to me it's obvious he himself has more provinces and magical gem income and armies than anyone else. Even if my globals stay up.
This will turn ugly, with players like Boron around... Either he's a master schemer trying to get a benefit from driving me to a corner, or just plain clueless and misinformed.