Design: antiluck charm
Knowing that Keggers lack the skill to shoot straight, and the ancient texts suggesting the existence of fortune magic, we have concluded that the Keggers are manipulating fortune. It is also noted that it is not actually possible to make weapons which are so accurate at such range with such projectiles.
Concluding that there is a magical means of manipulating luck, we have poured over our antimagic research and every mathemagical analysis that we have ever done with a certainty that there is a fortune component to magic and that it must be found. After spending months with massive prototype antimagic charms modified and focused, aiming exclusively at specific magical elements we have finally distilled the 'luck' aspect to magic. A thorough analysis leads us to believe that magical fortune is reciprocal. That is, it is shared by all entities influence by it. A gambler who wins a coin toss and their opponent who loses are both subject to the same 'luck' event, one receiving fortune and the other misfortune as parts of a single instance of fortune. Likewise, a wholly beneficial act, such as fair weather, Is distributed amongst all people who wanted a picnic, and opposed to everyone who prefers moody weather... Thus, it seems impossible to benefit from good fortune at the expense of another unless they are also subject to ill fortune.
We do not know anything about actually controlling it in any conventional sense, but we have specialised versions of our antimagic charms that instead of draining magic they only drain fortune. 'Luck', be it good or ill, becomes impossible within the area, which has been greatly increased over the now-old charms of before, and can protect an entire cannon and its crew. While we have concerns as to what this will do to morale, as exceptional successes often support the mood, it has become clear that the common Kegger is just too lucky...
Design: Ragnarok
We recall every wizard above apprentice level and Myark to a large, fixed, ritual circle within 100 kilometres of the target. They then spend a full two days generating the spell, which takes the form of a summoned quartz prism that contains fireballs, many, many, many fireballs. As many as every mage assembled(aside from Myark) can create over that timeframe(Assuming 500 wizards at one per minute over two days... 720000? They are loaded up with natural stimulants and kept awake and well-supported by a large staff of retainers, but sleeping can be completed after the great magic.) While Myark personally guides the overspell. The overspells is the conjuration of the prism at a remote location which, upon the spell's completion, appears with the total energy of the combined magic. Using Myark's superior mathematgical and trigothaumical abilities to visualise a distant target provided by redundant runners and scouts the prism can be materialised accurately... enough... at any point within 100 kilometres. At which point it typically falls towards the ground, but rarely has the stability to survive that long before releasing the assembled fireballs, trapped at the moment just after they began exploding.
May involve casualties and exhaustion amongst the casters...
1 fireball can blast a squad, 100 men, assume loose formation, 1x1 metre each, give them a circular pattern because too generous for my own good... Oh, lets be very generous and assume they are in spherical formation so the fireball has a volume of exactly 200 cubic metres. Do a little maths to add together the radius of all those balls... ... ... large?
Order, turn up the volume! All frost towers, maximum power!