To the kings, even the Rakshasas form is permissible. The Asura form is permissible to the Vaishyas and Shudras. Of the first five (forms), three are proper and two improper.
राज्ञां तु राक्षसोऽप्युक्तो विट्शूद्रेष्वासुरः स्मृतः। पञ्चानां तु त्रयो धा अधौ द्वौ स्मृताविह॥