Nevermind, got it. With 5 seconds left I had one jump on my back but i was able to shake it before it did any damage, and yes, you have to wait the entire time limit prior to recieving the achievement. I used the front yard so the toadstool ring would give me "some" safety. When i hit about 90 or so, the bull goblins or whatever came out.
Tips:
1) Use Simon and stay inside the ring. Hold "A" down until its at max pump on the splatter gun and hose anything on the line. You will only hit a couple at a time though. Sometimes 3 at most. the red ones take acouple of hits before they go down.
2) Use the 10 minute timer. Get to about 80 and then grind the clock down to a couple of minutes before making a push outside the ring or getting to 90pts.(thats when the bull goblins come out and they can throw stuff through the ring).
3) Use the "Will O' Wisp"! Since this has a distraction feature it makes it REAL helpful to get the goblins moving one way while you go looking for "Bell Flowers" (double damage). If you can stock pile a "Will O' Wisp", "Bell Flower" and a "Pond Skate"(Invincibility....cant miss them, they move real fast and are blue) you are in business and can move outside the ring with impunity and ride the time out while grabbing the last couple kills you need and collecting other "Will O' Wisp" to keep the goblins occupied while timeruns out.
SEATTLE/UW COG OWNER
Do you have COG?
People that are willing to trade security for freedom deserve niether.