To kill a Steam Tank, or at least damage it beyond the ability to be a serious threat. As usual it's best to combine magic and nonmagic strategies into a coherent approach.
Magic
Shadow: Best anti-tank lore. Pit of Shades, Penumbral Pendulum and above all Okham's Mindrazor will help you make the tank into a pile of scrap metal.
Death: Spirit Leech it as often as possible. Maybe a Purple Sun or two
High Magic: Swap spells for Spirit Leech and Searing Doom. Walk Between Worlds is the only anti-tank spell in the lore. Use it to stick whatever tank busting unit your army has right in it's face,
Wandering Deliberations: You already have Searing Doom and Spirit Leech from turn one. Now all you need is a Skink Priest to aim your spells. Your opponent will probably prioritize these with his dispels, so it’s hard to kill the tank outright with these two spells alone. Iceshard the tank while you are at it, it can shut down both the cannon and the steam gun. I would recommend having Plan B to engage the wounded tank with your Temple Guard bunker. Earthblood and Wyssans will both help you there.
Metal: Both direct damage spells do well, Enchanted Blades if good for when you engage it but it better be softened up first.
Life: You aren't going to kill it with magic, but you can buff the crap out whatever unit is fighting the tank to outlast it.
Beast: If you can get boosted Saurus heroes to fight the Tank with Savage Beast of Horrors, do so. Wyssans will help a bit. Curse of Anaheir can really hurt if they fail a dangerous terrain test (since Steam Tanks are technically chariots), but that's fairly luck based. You are generally better seeking a non-magical strategy if you are packing lots of Beasts.
Heavens: Heavens has lots of spells that will NEARLY do the job. Iceshard will nerf the shooting early on it but it won’t slow down the tank once it’s in close combat with you. Two spells hit with Strength 6 but that’s probably not enough. Even if you get both off every round that’s only 1 or 2 wounds per turn.
Fire: Fire will let you let you clear away Empire chaff without a lot of fuss. Now that you don't have Empire chaff to worry about. Use your Skink Skirmishers to pull every dirty redirecting trick possible.
Light: Redirect or tarpit the tank and hit the rest of the army. Light gives you a strong edge on every unit except the Steam Tank so play avoidance with the metal monster and go to town on everyone else.
Non-magic Solutions
Living Tanks: Carnsaurs will kill a STANK if you can avoid them being killed by cannons. Ancient Stegadons can severely damage a STANK if you get a good impact hit round, but the cannon danger applies. If you want to use your big dinosaurs better go full Monster Mash list for target saturation. Nice thing is no Empire unit is a good match up against big dinosaurs (except cannons...always cannons).
Magic wise this strategy mixes well with anti-cannon spells like Iceshard Blizzard and Pha's Protection, Walk Between Worlds to get your dinosaurs to the target faster, and Life for healing.
Elite Infantry: A large unit of Kroxigors can bash a tank fairly well. Temple Guard with the Razor Standard will do well too, and the aforementioned Razor Standard will work well against all four knight options, Great Swords and most Empire characters.
Magic wise this strategy works well with any buff spells that target whole units such as Enchanted Blades of Alban, Wyssan’s Wildform, and especially Okham’s Mindrazor. Hexing the tank isn’t bad either if you can dock it’s toughness or armor save.
Avoidance: You don’t have to engage the STANK, and this is the route I usually take if I find myself not taking a great anti-Tank lore. If the Empire player is not advancing much you can go around it. If the Empire player is playing aggressively, you can redirect the Tank with Skirmishers or tarpit in a Cohort.
Magic wise this strategy works well with defensive spells or low magic lists. It’s also a good strategy if the Empire player is keeping a level four Life mage near the tank at all times. Since most of the damage will be healed quickly, it’s probably not even worth attacking the tank until the mage is dead.
John Henry Approach: Scar Veterans or Oldbloods with strength 7 or above. They need a unit to absorb attrition damage from the tanks grinding but the Steam Tank will eventually die as long as your character (or ideal characters) cannot be individually targeted by the tank. This approach mixes well with Monster Mash or Elite Infantry.
Magic wise this strategy works well if you can boost the individual characters or hex the tank itself.
