Except that if he's ignoring 6's, he's only going to have like a 50/50 chance to have the spell go off. And that's IF he gets 6 dice (not saying he won't, but there's going to be times where it happens). Plus, on an unarmored, T3 mage, it seems like he should be relatively easy to take down with just RnF. Just push your dudes in there!
Well the last game I played he had a shadow wizard too and could just swap places with the death one to get him out of becalmings range. The problem is all of my dudes are dead before they can see combat thanks to the purple sun. Also, with the banner of sorcery the elf player will have a lot more dice than me.
The plague of dominion could work. It's a bit hit&miss, but still. Sallies having the unit flee is the same. Hit&miss, but works on occasion. CoC suicide charge is also a solution. The fellows are still resilient when facing the elves, unless said mage is hiding in a Swordmaster unit or something. Stegadon charges should be the bane of any and all mages foolish enough to stand in the way. I can think of a lot of ways to handle this. It's not hard, you just need to hit faster than the Archmage can get the spell off. Cheers!
a suicide skink chief with cloak of feathers and sword of hornet maybe could do the job. he would strike simultaneously with the elves. or give him a terradon instead of the cloak and the bane head for the freed up magic points. but if I would be the elf player, I would stick the mage into phoenix guard, which would make things a lot nastier....
blood statuette might be viable. forcing cupped hands of old ones on a casting of throne of vines is nice.
FYI, you choose becalming's target at the beginning of the magic phase - it doesn't matter if he moves around. Again, I'm not seeing this as an issue. It's one spell from one lore; it's hardly unbeatable.
also.... a mage in any unit will probably have a champion right next to him. if you throw characters at him he'll just challenge and you get to fight some champion who might even kill you. alltough, life is probably the key element here. throw dwellers below at his unit and he doesn't get a "Lo,S!" roll from it, 50% chance the mage will die, with cupped hands and/or throne of vines you can just throw 6 dices at it and hope for double 6's since it will rarely matter, and a miscast will probably kill fewer of your models than that mage will.