YAY! I managed to kill the dragon twice! First time with Divine Edge, second with Elixer but then it attacked again in a row and I had no items so I died. :(
For the people who keep dying randomly, is it because you might have neglected your bunker and it has been destroyed. I thought I was dying randomly but then I remembered to defend my bunker and I easily got the 200 kill badge using the SCAR.
 "Trigger Knight"){kind=icon}
 "Faultline"){kind=icon}
 "The Endless Zombie Rampage"){kind=icon}
 "Fragger"){kind=icon}
 "Continuity"){kind=icon}
 "Protector"){kind=icon}
 "Snail"){kind=icon}