Check spelling carefully:
Step 1: Option A - Accomplish
Correctly spelled. Means to successfully complete something.
Step 2: Option B - Mischevious
Correct spelling is "Mischievous.''
Option B has an extra 'i' after 'ch' and incorrect vowel placement.
Step 3: Option C - Dilemma
Correctly spelled. Means a situation requiring a choice between options.
Step 4: Option D - Subtle
Correctly spelled. Means delicate or not obvious.
Therefore, Option B is the incorrect spelling.