irresistible — SB 1.12.21plugin-autotooltip__small plugin-autotooltip_bigŚrīmad Bhāgavatam 1.12.21

Amongst great bowmen, this child will be as good as Arjuna. He will be as irresistible as fire and as unsurpassable as the ocean.

unconquerable — SB 4.22.57plugin-autotooltip__small plugin-autotooltip_bigŚrīmad Bhāgavatam 4.22.57

Mahārāja Pṛthu was so strong and powerful that no one could disobey his orders any more than one could conquer fire itself. He was so strong that he was compared to Indra, the King of heaven, whose power is insuperable. On the other hand, Mahārāja Pṛthu was also as tolerant as the earth, and in fulfilling various desires of human society, he was like heaven itself.

approachable with great difficulty — SB 10.2.17plugin-autotooltip__small plugin-autotooltip_bigŚrīmad Bhāgavatam 10.2.17

While carrying the form of the Supreme Personality of Godhead within the core of his heart, Vasudeva bore the Lord's transcendentally illuminating effulgence, and thus he became as bright as the sun. He was therefore very difficult to see or approach through sensory perception. Indeed, he was unapproachable and unperceivable even for such formidable men as Kaṁsa, and not only for Kaṁsa but for all living entities.