Divide these sixteen words into four groups based on something they have in common. You'll find that each of the four groups gives you a clue leading to something in particular. The words aren't in any particular order.
WELL, PACE, WITCH, WADE, CLOUD, PLANETS, TAR, FLUORINE, SCOPES, ANGER, EVIL, LIVES, HIP, HOOT, BROWN, RUGGED
Once you've figured out the groups and the thing the wall is cluing, answer me this: What is small and causes problems?
This puzzle is dedicated to @matt/@merrybot, with permission!
The groups are cluing something to do with Matt's favorite media franchise.