What does Mike ACTUALLY think about Riley?

He loves her,but they never talk. So he doesn't know how Riley feels.

How does Mal feel about Riley, if he has any feelings?

He does have feeling for her but, in a twisted way. When they first meet he loved the face she made when she was scared so he tried to make her have that look a lot. Now his feelings have grown stronger,I guess you could say he loves her. Mal and Riley's relationship might grow stronger or fall weak. You never know!

If Riley is deemed mentally unstable, what kind of treatment will they prescribe for her?

She was determined mentally unstable. She might either go to treatment about her not 'hurting herself'. If not I will have to come up with what else.

Why did Mal carve his name in Riley's arm?

Mal mainly gave her the 'brand' so will think she is crazy and so she can stay with him. Second he did it to make Mike angry, physically hurting Riley's while she was unconscious made Mike him furious.