恁 is literary (found in Song-era ci poetry like 辛弃疾) and survives today in Henan / Central Plains dialect, where it also serves as a second-person plural 'you all'. In standard Mandarin writing it feels archaic.
usage
Read nèn for the 'such / so' meaning; old texts also use the reading nín as a variant of 您. Dialect speakers often stack it: 恁大 (that big), 恁多 (that much).
