Firstly: Fasting the Day of `Arafah
It is makruh for a pilgrim to fast the Day of `Arafah. It is mustahabb for a pilgrim not to fast. This is the position of the majority: the Malikis, Shafi`is, and Hanbalis.  Hanafis deem it makruh for a pilgrim to fast if it weakens them.
Secondly: Offering Optional Prayers between Zuhr and `Asr in `Arafah
It is makruh to offer optional prayers between zuhr and `asr in `Arafah. This is by agreement of the four schools of jurisprudence.