-Make a dual red/orange level 5. -Up it until its level 8. -Make a dual yellow/white, place it behind the or/red to make sure the mana gem has plenty of time to gather mana before creeps dies. -puts the red/orange to swarming first. -Always use tower beam on the mana gem and use tower barrage on yellow/white gem. Beam on mana gem will give you ridiculous amount of mana in no time.
Thats it. You need to have enough starting mana to put tower+level gem, the rest can go into skill.
At level 7 the yellow/white already insane amount of damage, level 10 one is enough to kill anything in looming. Yellow will make you do 80% chacne of doing x75 damage and white will upgrade the base damage by a ton.
I think its k6, im not sure really, but i remember getting beam before curse. Its already unlocked in V1(the level where you cant haev skillpoints or talismans) so it should be close to that.