***You can buy other upgrades after purchasing Elf Supply Drop 1, but DO NOT BUY Improved Power, or you will have problems with kids with guns (Gorillaz track lol) at wave 10, they somehow (bug) will outrange you and shoot you beyond screen (also not with them, my primary weapon became useless because of high knockback)
*** Max out reload, crits and luck
***After wave 10 you may play endless mode for 1-2 times to gain a TONS of money and purchase Elf-O-Matic, Candy Cane Turret and Poo Mortar (at once!). After you can decide what you will upgrade by yourself, because EASY GAME->EASY WIN. LAST LEVEL PASSED QUITE IMMEDIATELY :D
This is a kinda fun game, but cointain some bugs, if you play properly you will aquire medium achievement pretty fast.
*** First, buy Dual Teagles (this was my first and last primary weapon) and focus on Scavengers elves (for money).
*** Upgrade Teagles on wave 4.
*** After finishing with the Scavengers focus on Elf Supply Drop (ATTENTION: for some reasons (bug) I couldn't use second spell till I figured out that I need to purchase Jack Frost for one time)
Interesting bug: If you call fireteam and after recharge Cooldown and call 'em again, this team will stand forever on the battlefield as a shield (it's damage 0 after buff is gone, but you can call 'em after, they will still remain and make a damage )