An imperative can be reinforced with the heavy emphatic nūn, recognised by its shaddah. A regular singular then has fatḥa before the nūn, while dual and plural forms undergo their own changes.
Word / formMeaning / explanation
اِفْعَلْ → اِفْعَلَنَّdo it definitely!
لِيَفْعَلْ → لِيَفْعَلَنَّlet him certainly do.
اِفْعَلُوا → اِفْعَلُنَّyou men must certainly do.
Masculine plurals have ḍamma before the heavy nūn; feminine plurals use a separating alif. A single ending cannot simply be pasted onto every person form.