You get the harpoon at level 12 not 9. :o *edit* Oh, I thought you were at the final boss which is level 15, at level 9 is the first boss. To kill that boss you need to use Trigger Plates in order to shock his head and make him open the eyes on it's tail. When the eyes are open they can be damaged by the main turret and mini-me's and deal 25% of the boss max health as damage when destroyed. You must build a medium-large maze with a minimum of 4 trigger plates since you want to make him open his eyes 4 times. Also, make sure the mini-me projectiels won't be blocked by his tail.
There is a comment made by MichaelChandra which has a layout example ( https://i.imgur.com/wrAQKjn.png ) kinda spoilerish though. If you want some tips then you can try using harpoons with the decimator upgrade and place disruptors in the place where the boss will be pinned down. :o
Gold multiplier is useless.
For example, green gold multiplier give 25% over 20 minutes, it's equal to 5 minutes of gold.
Green warp give 30 minutes instantly
You can work to get more heroes, or try upgrading your peasants smash ability, so that they can kill the powered up drakes. If none of those are helping, perhaps a soft reset?
 "Zero IDLE"){kind=icon}
 "Rogue Isles"){kind=icon}
 "Spacedust Defender"){kind=icon}
 "Enchanted Heroes"){kind=icon}
 "Crusaders of the Lost Idols"){kind=icon}
 "SAGA Idle"){kind=icon}
 "AdVenture Capitalist"){kind=icon}
 "Realm Grinder"){kind=icon}
 "Dungeon Warfare"){kind=icon}
 "The Wizard"){kind=icon}
 "StrikeForce Kitty"){kind=icon}
 "Decision:Medieval"){kind=icon}
New content is constantly in development. Next update is going to bring 10th level and some new achievements