Rishi: Vājasaneyin ritual tradition (school attribution).
Devata: Apāmārga (as a deified plant-power) and the general expiatory force of ‘apa’ (removal).
Chandas: Anuṣṭubh-like (to be verified); compact expiatory verse.
Samhita Patha (Devanagari)अपा॒घमप॒ किल्वि॑ष॒मप॑ कृ॒त्यामपो॒ रप॑: । अपा॑मार्ग॒ त्वम॒स्मदप॑ दु॒:ष्वप्न्य॑ᳪ सुव
Transliterationapā́gham ápa kílviṣam ápa kṛtyā́m ápo rápāḥ | apā́mārga tvám asmád ápa duḥsvápnyaṃ suva
Translationขอให้ความชั่วร้ายจงไปเสีย ขอให้บาปจงไปเสีย ขอให้ไสยเวทจงไปเสีย ขอให้มลทินจงไปเสีย โอ อปามารคะ (Apāmārga) ขอท่านจงขับไล่ความฝันร้ายออกไปจากพวกเรา
Padapatha (Word Analysis)अप । अघम् । अप । किल्विषम् । अप । कृत्याम् । अप । रपः । अपामार्ग । त्वम् । अस्मत् । अप । दुः-स्वप्न्यम् । सुव
Word by Wordअपाघम्(remove) the blemish/evil कृत्याम्witchcraft, harmful rite अपामार्गO Apāmārga (the plant/personified remover) दुःस्वप्न्यम्bad dream, nightmare (evil of bad dreaming) सुवimpel/drive (it) away; set (it) forth 
Entities MentionedA
Apa (apah—‘removal’ as an apotropaic force) Viniyoga (Ritual Application)