Crimon Gaurdian training?

Sure it would work, just like training anywhere can give you exp. Is it the best exp a mage can get? No. Getting hit by consant 3k+ damage and getting sealed isnt exactly going to speed up your training or help your pot costs. The more HP the monster has (for a lower lvl arch mage), the worste off a mage will be training there, due to how slow ultimates are. If you take 5+ hits to kill a gaurdian, then even though you're attackin the whole map it won't net you a good exp per hour. Newties or wyverns (for ice mages) are still the best exp for a mage spammin ultimates. Using demon to train for a mage is just slow..