First you gonna plug the haze. To do it you need the tier 2 black ant shovel which you need to use to get the chewed gum. Climb onto the weed killer tank and plug the haze with the gum.

Now you need to find an aphid. The best spot to be looking for one is near the oak, as you will not need to dodge its terrific attacks for too long.

After finding one, try to lure it near the oak, as our secret weapon is there. It may be hard to dodge the aphid but the closer you are to the oak, the easier it will be for you.

The last step is to find an infected wolf spider, and let it kamikaze you with the aphid, by bombing you with shrooms. It worked 9/11 times for me so I think it's pretty reliable.

I hope this helped you to kill the beast and if you liked the guide make sure to like and award me. Thanks!