Magicka Challenge Mode

Outside of Magicka: Vietnam, the rest of challenge mode is the same.  Pick an arena and a set of allowable drops (which can be unrestricted...), and battle against 20 waves of enemies.  You can bring up to three allies with you, but so far I've just been going solo.

The format and scoring system is fairly similar to the Last Stand mode of Warhammer 40k: Dawn of War 2.  Enemies enter the arena from fixed locations.  You have a multiplier that goes up as you kill stuff and goes down as you suffer deaths.  The difference lies in the drops I previously mentioned.  During each wave, one or more chests will spawn.  They then grow legs and proceed to wander about the arena.  They can bite you and deal damage to you as well.  Destroying the chest makes it drop an item or a magick.  Thus, you're at the mercy of Magicka's random number generator concerning what you're going to get.

That said, it's very possible to develop working strategies, that change depending on the drops you get.  My staple for the very beginning when I have nothing is ARSE mines.  They allow me to play a game of control, where the enemy can't kill me because they can't get to me.  As I gain magicks, I'll adapt as necessary.  On several occasions I've gotten both Invisibility and Summon Elemental.  If that happens, anything's possible.

As far as weapon drops go, Invisibility can be rendered less necessary if I'm fortunate enough to receive the Scepter of the Troll King, which makes enemies prefer other targets.  However, that only works if I can summon other targets for them to prefer.  Fortunately, if I don't have that ability yet, its active ability allows me to charm an enemy, which comes in handy even if I have Charm, seeing as how it just takes one click to charm something with the active ability, compared to inputting WED spacebar to use Charm...

My suggestion is to find the stuff you prefer, and then turn off all the categories that don't contain it, so you have a better chance of getting what you like.

I'll give a rundown of spells, magicks, and weapons I've found to be useful.

• Spells
• ARSE regular cast (or area cast if you have Teleport) - I used to use this on weapon cast as well, but...
• QREASR weapon cast - Be very, VERY careful with this one.  As in, come to a complete stop when you swing your weapon to actually cast it.  And then high-tail it in the other direction.  This spell deals massive damage.  Doing any other cast method with this spell is suicide.  Also, it'll get you the achievement for having 5 elements in one spell if you haven't already gotten it some other way (using Steam...).
• QFASA (or QFQFASA...) regular cast - Go-to beam for killing chests.  Also works wonders on anything that's been frozen.
• QFQFQFQFQF area cast - If you have frost elementals around and you don't have Rain, support them by area-casting this.  It will wet down your enemies, which the elementals will then freeze on their next hit.  What's better than an enemy that moves very slowly?  An enemy that can't move at all.
• EQRAF self cast - Inputting the F at the end melts the Ice back into Water, allowing you to have a shield that protects against both Water and Lightning.  Handy for casting Thunderstorm and then being able to conjure Lightning while being immune to the lightning strikes from Thunderstorm at the same time.
• Magicks
• Haste/Teleport - Mobility is king in this mode.  If you can avoid the damage, you'll stay alive.  Simple as that.
• Invisibility - If they can't see you, they can't target you.  It doesn't render you impervious to damage, and doing anything other than movement or conjuring will make you visible again.  Still, it's nice to have around.
• Charm - Temporarily turning one of your enemies into an ally is not to be underestimated.  Especially because you can charm a powerful enemy, then wet them, freeze them, then lightning beam them without having to worry about retaliation...
• Summon Elemental - What's better than killing things yourself?  Summoning magical beings to do it for you so you can sit back and relax for a while.  I prefer frost elementals myself, because of my aversion to playing with a control strategy.  There are a couple waves you have to look out for with frost elementals though, so it's not perfect.  I would advise against summoning more than one type of elemental, because the dominant type will kill the minority type.  Also, if they're all one type, they'll heal each other and you'll only need to worry about them on the waves with the grenade guys (11? and 20).
• Blizzard - If you have Summon Elemental and want to produce a bunch of frost elementals quickly, cast this and then spam Summon Elemental (well, as fast as you can type SEDQFS and hit spacebar...).  Blizzard will automatically turn them into frost elementals for you.  Toss up a quick ER self cast before casting so you won't freeze yourself.
• Rain - Wets enemies, letting frost elementals freeze them in place.  Affects the entire arena, so you don't have to worry about it not hitting something.  Toss up a quick EQ self cast before casting, so you can still conjure lightning.
• Raise Dead - Not as useful as Summon Elemental, but anything that puts targets out there that aren't you is worth having around.  Note that some enemies are immune to poison.  They won't damage those enemies, but they will still surround them and block their movement, which is still useful.
• Conflagration - Spiders absolutely hate fire.  Just so you know.
• Thunderbolt - When it hits what you want it to hit, it works wonders for eliminating a single target.  It can get confused with lots of elementals about though.
• Staves
• Scepter of the Troll King - Active charm ability, plus the passive ability of making enemies prefer other targets, makes this staff precisely what you want if you can summon anything at all.
• Staff of War - Double HP plus physical resistance.  Need I say more?  The active Arcane Bolt ability recharges pretty quickly and shouldn't be forgotten about.
• Daemon Arm - While it's one of the best in Adventure, it's not as useful here, because you'll need to be moving a fair amount of the time.  Still, when you've got it down to that one last enemy, you can pop off a beam and let 'er rip.  Only marginally useful, just mentioned it so I could say that.
• Gnarled Staff - Active ability summons trees to fight for you.  Great if you don't have any magick that summons anything and you're not up against a wave that deals fire damage.  The summon ability has a long recharge though, so you'll have to support them.  Note that you can heal them.  Area cast heals work best, but risk healing your enemies at the same time.
• Weapons
• Knife of Counter-Striking - It took me way too long to figure out what this weapon was referencing.  It's referencing the knife in Counterstrike, where if you're carrying it you can run faster.  Having this weapon essentially gives you a permanent Haste, which is indispensable.  Especially considering that you can still Haste yourself while wielding it, and the effects stack...
• RPG-7 - Don't underestimate the value of 3000 damage in a single spike.  True, some spells can out-spike this, but it's a worthwhile weapon nonetheless.  Just make sure you've got some distance on your target, and don't forget about the manual reloads (and the length thereof...).

I've gotten to wave 20 twice solo, and died on wave 20 twice solo for entirely stupid reasons.  The first time I stepped on one of my own ARSE mines by accident and couldn't thaw, heal, and cast Invisibility fast enough, and the second time I was trying to cast Blizzard and summon more elementals and got hit by stray grenades.