A passive imperfect has ḍamma on the imperfect prefix and the basic pattern يُفْعَلُ. Adding emphatic nūn does not turn the passive voice into active voice.
Word / formMeaning / explanation
لَيَفْعَلَنَّhe will certainly act (active).
لَيُفْعَلَنَّthe action will certainly be done to him (passive).
لَتَفْعَلِنَّyou, one woman, will certainly act (active).
لَتُفْعَلِنَّthe action will certainly be done to you (passive).
The grammatical participant changes, but the emphatic meaning remains.