Assaillir belong to the 3rd group.
Assaillir is conjugated the same way that verbs that end in : -aillir
Assaillir is conjugated with auxiliary avoir.
Assaillir verb is
direct transitive. Assaillir verb is a direct transitive verb, so passive voice can be used.
Assaillir is a french third group verb. So, this verb is irregular and do not follow a regular conjugation pattern like first or second group verbs. Follow this link to see all the endings of the conjugation of most of the third group verbs : conjugation rules and endings for the second group verbs.
ASSAILLIR : v. tr. Attaquer vivement par surprise. Assaillir un camp. Assaillir les ennemis dans leurs retranchements. Nous fûmes assaillis d'une grêle de pierres. Fig., L'orage nous assaillit. Nous fûmes assaillis d'une furieuse tempête. Jamais tentation plus dangereuse n'assaillit mon cœur. Tous les malheurs l'assaillirent à la fois.