In heteroleptic complexes, always use the crystal field theory to find hybridization and magnetic behavior. Don't use the concept of forced pairing and all Coz there will be a 90% probability of the wrong answer for most of the standard question of such type.

use the concept that presence of strong ligand, cheating ligand, a central atom of 4d and 5d series,....

PLEASE READ NCERT BOOK (UNIT 9: CO-ORDINATION COMPOUNDS) There are a lot of examples available