To beat day 3 on hard just evenly space your flamers and have them all in the same direction, use the "E" key to make sure there spread covers everything. Your first 600-900 Points that you earn (spend all starter points on flamers) can be spent on more flamers but you'll wanna be careful of the bursters that come in later waves, a flamer will die if a burster dies in flamer range of them. After you set up your flamers just mass nailgunners behind them, if you can get a thick enough wall of nail gunners up the nailgunners CAN kill hunters, it just takes alot of shots. If you have say 15 shooting each time a hunter pops up though... well it dies instantly, they don't even have to shoot again. Somehow I never had any difficulty on day 3 :/ I wish anyone who's struggling good luck.
Below method proven to work on Hard, although my right side started to crumble a bit at the end it held together. Make sure all angles are covered and maybe have some guys in the back angled to kill hunters who start chewing their way through 11 of your guys -.-
Recipe for success on final wave? Get a front line of flamers, a mid section 2 rows thick of gunners, and a row imploders directly behind your imploders. Your troops SHOULD clog up the screen for all those rows. Also, behind all these guys just sporadically place fuel launchers and flare gunners, if you get enough of these placed every single enemy gets set on fire. The imploders knock back everything, the flamers hypothetically kill whatever isn't knocked back (everything is knocked back) and the gunners/flaregunners/fuel launchers do the actual killing.
Hope this helps anyone who feels stuck :)
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