This one is actually a little tough. Reaching the point plateau should be your only real concern, if you play aggressively, the other Worrior will lose all their lives...and you'll likely be well beyond 3x their score by then.
If you're aggressive in chasing down and killing the blue Burwors, and killing the other Worrior whenever you can, it's just a matter of killing off the yellow Garwors and red Thorwors to progress. When things got hectic, I sat in a corner on the right and jammed the fire button.
The bug-like Worluk appears in the third and fourth "double points" stages, and will escape through the doors on the edges of the screen. He's worth a good number of points if you can kill him.
It took me 3 or 4 tries, but I was able to get it on the fourth stage.
My game totally took a dump when the achievement unlocked, though. It slowed to a crawl, and even though I wanted to continue playing, I had to pause the game exit to the game select menu.
This game is an absolute blast, and a sorely overlooked title.