I suggest using a Jester with a Propeller Cat and an Ember Scepter together with a Monk using a Fairy for the boss. If you don't have a good Ember Scepter, then the Monk will be the main damage dealer, in that case a Jester with a Propeller Cat plus a Monk with a seahorse pet is the advisable.
The Dragon has 3 different phases
- First half of Dragon's HP: Demon Lords will continously being summoned from random spawns around the map. They are summoned after fixed ammount of times, so the best strategy here is to ignore the Dragon as soon as you see a Demon Lord on the mini map, then run and kill it as fast as you can, then go back again to the center to continue attacking the dragon. Usually you will end up killing 2~4 Demon Lords depending on how fast you damage the Dragon. Do NOT ignore the Demon Lords, otherwise they will melt your minions.
- Half of Dragon's HP: Dragon becomes invencible and summons a Kraken; Demon Lords will not spawn anymore during this stage, but be careful to make sure no Demon Lord appeared right before the Kraken is summoned. If you take way too long to kill the Kraken's tentacles, they will all regrow; also the Kraken from time to time does a spin attack that will throw you to the edges of the map (right before this spin attack he will move closer to you, just walk a little away and you will avoid it easily). Besides that it's important to have in mind that the Kraken does WAY too much damage, so you can NOT "face tank" him for too long, try to keep some distance while attacking, the Seahorse and the Jester will be the main damage dealers to the Kraken, but if your Monk has a ranged weapon that will be helpful aswell. This is by far the hardest part in this map, this Kraken is the only real challenge here, so if you feel the need to, feel free to add healing auras in every other spot besides the center so you can try to run away in case of emergency, but be VERY careful if doing so, because you will most likely lose if it happens for the Kraken to aggro in any of your building spots, he will simply melt the Ogres, so play safe and be smart.
- Second half of Dragon's HP: So you killed the Kraken, congratulations, but it's not over yet (but at the same time, not far from over). Now the Dragon is not invulnerable anymore, but he will instantly summon 2 Demon Lords after the Kraken's death. If you are playing solo, or if your DPS isn't too low, your best bet will be to rush the Dragon down, but if you are playing together with a Monk DPS or you feel your DPS is in fact too low, then each of you should run to kill a Demon Lord each before finishing the Dragon off. No big deal at this part. Good luck.