If one observes Lalitōpākhyāna attributed to Brahmāṇḍa Purāṇa, one can see that Viśukra was killed by Mantriṇī or Rājamātaṅgī:
विशुक्रं योधयामास श्यामला कोपशालिनी |
अस्त्रप्रत्यस्त्रमोक्षेण भीषणेन दिवौकसाम् ||
महता रणकृत्येन योधयामास मन्त्रिणी |
आयुधानि सुतीक्ष्णानि विशुक्रस्य महौजसः ||
क्रमशः खण्डयन्ती सा केतनं रथसारथिम् |
धनुर्गुणं धनुर्दण्डं खण्डयन्ती शिलीमुखैः ||
अस्त्रेण ब्रह्मशिरसा ज्वलत्पावकरोचिषा |
विशुक्रं मर्दयामास सोऽपतच्छिन्नविग्रहः ||
In the same chapter of Lalitōpākhyāna, the slaying of Viṣaṅga by Daṇḍinī or Mahāvārāhī is also described:
विषङ्गं च महादैत्यं दण्डनाथा मदोद्धता |
योधयामास चण्डेन मुसलेन विनिघ्नती ||
स चापि दुष्टो दनुजः कालदण्डनिभां गदाम् |
उद्यम्य बाहुना युद्धं चकाराऽशेषभीषणम् ||
महामुसलदण्डाग्रघट्टनक्षोभिताम्बरौ |
अयुद्ध्येतां दुराधर्षौ दण्डिनीदैत्यशेखरौ ||
अथाऽर्धरात्रसमयपर्यन्तं कृतसङ्गरा |
संक्रुद्धा हन्तुमारेभे विषङ्गं दण्डनायिका ||
सा तन्मूर्ध्नि निमग्नेन हलेनाऽकृष्य वैरिणम् |
कठोरं ताडनं चक्रे मुसलेनाऽथ पोत्रिणी ||
ततो मुसलघातेन त्यक्तप्राणो महासुरः |
चूर्णितेन शताङ्गेन समं भूतलमाश्रयत् ||
However, Lalitā Sahasranāma describes the death of Viśukra at the hands of Vārāhī and Mātaṅgī slaying Viṣaṅga:
मन्त्रिण्यम्बाविरचितविषङ्गवधतोषिता |
विशुक्रप्राणहरणवाराहीवीर्यनन्दिता |
Some have tried to argue that the above two names in the sahasranāma are corrupt and that the original form of these names is in sync with the tale narrated in Lalitōpākhyāna. However, such an argument holds no strength in the light of acceptance of the above two nāmas by all commentators on the Sahasranāma, including Bhāskararāya Makhīndra. Though this one aspect of controversy gets oft-discussed, one should also observe the next nāma:
कामेश्वरमुखालोककल्पितश्रीगणेश्वरा |
The above name describes the episode of āvirbhāva of Mahāgaṇapati and the destruction of Vighna-yantra by him. However, in Lalitōpākhyāna, it is said that Viśukra constructed the yantra named Jayavighna at the order of Bhaṇḍāsura:
उवाच वचनं भण्डः जहसारुणलोचनः |
विशुक्र भवता गत्वा मायान्तर्हितवर्ष्मणा ||
जयविघ्नमहायन्त्रं कर्तव्यं कटके द्विषाम् |
इति तस्य वचः श्रुत्वा विशुक्रो रोषरूषितः ||
मायातिरोहितवपुर्जगाम ललिताबलम् |
शिलापट्टे सुमहति प्रालिखद्यन्त्रमुत्तमम् ||
अष्टदिक्ष्वष्टशूलेन संहाराक्षरमौळिना |
अष्टभिर्दैवतैश्चापि युक्तं यन्त्रं समालिखत् ||
आलसा कृपणा दीना निद्रा तन्द्रा प्रमीलिका |
क्लीबा च निरहङ्कारा इत्यष्टौ देवताः स्मृताः ||
देवताष्टकमेतच्च शूलाष्टकपुटोपरि |
नियोज्य लिखितं यन्त्रं मायावी सममन्त्रयत् ||
पूजां विधाय यन्त्रस्य बलिभिश्छगलादिभिः |
तद्यन्त्रं वैरिकटके प्राक्षिपत् स महासुरः ||
It was to destroy this Jayavighna yantra created by Viśukra that Lalitāmbikā created Mahāgaṇēśvara. The episode of the creation of this yantra and its subsequent destruction by Mahāgaṇapati occurs in Lalitōpākhyāna before the episode of destruction of Viśukra and Viṣaṅga. The sahasranāma however, lists the names related to āvirbhāva of Mahāgaṇapati and the destruction of Vighna-yantra after the name dealing with the slaying of Viśukra. This is one of several discrepancies seen between Lalitōpākhyāna and Lalitā Sahasranāma.
In the past, when a question was posed before Srī Saccidānanda Shivābhinava Nr̥simha Bhāratī in this regard, he smiled and replied, ‘Does it matter? There are several such discrepancies between the tales narrated in various purāṇas. But if you want a practical answer to satisfy your curiosity, my choice would be to go with Lalitā Sahasranāma’. H H also favors the sahasranāma because of its origin from Vaśinyādi Vāgdēvatas, who represent verily the speech of Lalitā Parā Bhaṭṭārikā. Moreover, Sahasranāma is not merely a stotra but also a mālā-mantra. The importance of Sahasranāma over other pramāṇas was also illustrated by HH when someone questioned him regarding the structure of bīja, śakti, and kīlaka for Pañcadaśī mantra. H H, after nine days of discussion with several scholars from Gauḍa, Gurjara, etc., concluded that the pramāṇa of sahasranāma, which also matches what is described in Dakṣiṇāmūrti Samhitā and the tradition of Sringeri maṭha, is acceptable (as against other Tantras such as Paramānanda), based on the names: śaktikūṭaikatāpannakaṭyadhōbhāgadhārinī, etc.
In our opinion, this issue is really not worthy of deep contemplation or discussion. If it was, the invincible Bhāskararāya would hardly have ignored it in his magnum opus Saubhāgya Bhāskara.