I've yet to come across a reliable sunni scholar praying for Yazid's mercy, some went as far as to say that he was a disbeliever because of the remarks he made after the martyrdom of Imam Hussain [radi'Allahu anh]. From amongst those, Taftazani, Alusi & Ibn Aqeel. Others suggested that there was no proof for his kufr & refrained from sending la'na upon him, like al-Ghazali. Abu'l Faraj Ibn Jawzi has a work refuting those who condemn the dispraise of Yazid called 'Al-Raddu alal' muta'asib il aneed, al-maani min dhamî Yāzid'. What is absolutely certain is that he was a fasiq & fajir, Allah Almighty give him his just deserve [& the Shi'a who supported him].