totally focused , without regard to anything else
That skateboarder was fiendishly focused on that trick.
by thunderzap November 26, 2011
To fiendishly shadow is to watch hentai for over 48 hours, and only stopping to eat. Frequent fiendish shadowers will often become fiends, and will normally be morbidly obese because of the nature of the activity.
Wow, fiend was actually fiendishly shadowing last week. I thought he was just sick, but he still smells like cum and pizza.
by CowCentralTootToot February 28, 2019