Why do Shias invoke Ali when making Dua? Is it due to their belief that mentioning him increases the likelihood of their Dua being fulfilled or because they attribute a certain special status to him?
We invoke Ameerul Mo’mineen Ali (AS) because he is the most humble servant of Allah (SWT) after the Prophet Muhammad (SAWA). We believe that his Du’a for us has greater weight in front of Allah (SWT). In Quran, sins of Proohet Ya’qoub (AS) requested the father to seek forgiveness from Allah for them and he accepted their request and promised to pray for their forgiveness (Sura Yousuf , verse 97).
The Du'a of Ameerul Mo;mineen (AS) for us is a great blessing.
Wassalam.