Here is the commonly recited mantra of the 13th Tirthankar, Bhagwan Vimalnath:

Devanagari: ॐ ह्रीं श्री विमलनाथाय नमः ।

Transliteration: Om hrīm śrī Vimalanāthāya namaḥ.

Meaning (arth): “I bow with reverence to Bhagwan Vimalnath, the perfectly pure (vimal) Arihant, to awaken those same pure virtues within me.”

Notes on tradition:

• Both Shvetambar and Digambar traditions hold the Navkar (Namokar) Mantra as primary for all Tirthankars. Many devotees first recite Navkar, then this short Vimalnath mantra.
• In practice, minor variations exist (for example, with or without “śrī” or the bīja “hrīm”): “ॐ श्री विमलनाथाय नमः” or “ॐ विमलनाथाय नमः.” The spiritual intent remains the same—humble salutation to the Tirthankar’s virtues.

For a brief profile of Bhagwan Vimalnath, see this reference from JainKnowledge: