Here are the possible solutions for they sometimes intrude at weddings and also in this puzzle's theme clue
Answer
Clue
Relevancy
exes
Clue
They sometimes intrude at weddings, and also in this puzzle's theme
Definition
EX, to cross out
four
Clue
Number of times this puzzle's theme word appears diagonally in the grid (to complete the puzzle, shade those words plus the Down answers that begin where they meet)
Definition
the cardinal number next above three
lllllllllllllllllllll
Clue
Much of the Smurfs' theme song, and this puzzle's theme
familyfeud
Clue
"Something you would cheat on if you knew you wouldn't get caught." "___" (also, the source of this puzzle's theme answers)
mandms
Clue
Mars mouthful; also, a hint to this puzzle's theme
wordladder
Clue
Puzzle invented by Lewis Carroll (and a hint to this puzzle's theme)
ideas
Clue
Sometimes they're good, sometimes they're harebrained