The passive imperfect يُرْمَى changes shape when an emphatic ending attaches:
Ordinary formHeavy nūnLight nūn
يُرْمَىلَيُرْمَيَنَّلَيُرْمَيَنْ
تُرْمَىلَتُرْمَيَنَّلَتُرْمَيَنْ
أُرْمَىلَأُرْمَيَنَّلَأُرْمَيَنْ
These are emphatic forms, not the subjunctive after lan or jussive after lam. The derivational reason is therefore different. Do not treat a dash in a light-emphasis table as a usable alternative form.
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Full Conjugation of the Yāʾ-Final Verb رَمَى يَرْمِي
The passive imperfect يُرْمَى changes shape when an emphatic ending attaches:
Ordinary formHeavy nūnLight nūn
يُرْمَىلَيُرْمَيَنَّلَيُرْمَيَنْ
تُرْمَىلَتُرْمَيَنَّلَتُرْمَيَنْ
أُرْمَىلَأُرْمَيَنَّلَأُرْمَيَنْ
These are emphatic forms, not the subjunctive after lan or jussive after lam. The derivational reason is therefore different. Do not treat a dash in a light-emphasis table as a usable alternative form.