[HoneyBadger]

I'd like to advance the idea that, just because their aren't currently tactics to use against the Van, Helheim, that most people can agree are acceptible, doesn't mean that they have to be Nerfed, it could just mean that more tactical/strategic options should and could be added that would focus on Van and Helheim's weaknesses without making them objectively any weaker.
Beat them the same way you'd beat any real-world unbarded calvalry-whether they were invisible or not-with field fortifications or phalanx. Unfortunately, we don't have a way yet to create fieldworks or field artillery or even simple ditches or stake-rows, but you can still use lots and lots of cheap units with long sticks, and eventually they'll get through the glamour. A scriptable "form phalanx" command with slow or no movement and a strong advantage against calvalry would be a start, that or a "set pikes" function which did the same thing, would be good. Magic would serve to ensure that phalanx-formations didn't dominate battlefields, but at the same time, they'd be an effective, obvious, and realistic choice against quite a few high-powered units, Van and Helheim included.

Another idea along this line is to have "landmine" type spells. I mentioned this earlier in another post, but basically it would be spells that remain placid-or even undetectable-until units contact them, at which point they go off, doing whatever effect they do. It's another fairly obvious use of, this time, battlefield magic, and it would make sense that wizards and whatnot would develope spells that would support an army while allowing the weak wizard to get well away from the conflict and danger, atleast as far as behind some bodyguards. To keep this type of magic from getting out of control, it could automatically vanish if the casting wizard is struck by arrow, spell, melee, whatever. In the meantime it would be great at breaking up charges and unaffected by Van glamour.

A third way to stop Van is if the glamour wasn't effective against blind or darkvision foes.

A fourth way is to give archers the command "target mounts". This would enable archers to concentrate on a target's trusty steed, which is a lot easier to hit than a Van, glamour or no glamour. You could also have them use British infantry tactics, with crossbowmen shooting standing, with a row of crossbow kneeling and firing and a third row behind them reloading/waiting to fire, with a command such as "Missle Volley". Put a couple rows of stakes in front of them (I'd really like to see units have the "Defend Position" command) and Van would have bad days all over the place. It wouldn't even be unfair to Helheim, because Valkyries could still fly over the defenders.

It would be nice if units gained more advanced tactical options, such as "Defend Position" and "Target Mounts" as they and their leader gained experience. Does anyone know if units in hills or woods recieve a defense bonus? If not, that'd be a great ability to add to the game. I know some units suffer from being in a swamp, but it seems like more experienced, elite forces would know to defend themselves well, and fight better, by taking advantage of their surroundings. Naturally, magic could only add to the potential for defending positions.