@ana993 I absolutely think they went with the right choice leaving any "known face" out of the mix: the Doctor knows already everything the universe can conjure would be a trick, and instead it went with something personal for itself; it knows the Doctor would be more intrigued by an honest friend instead of a manipulating one, and this makes their last goodbye poignant.
Shout by AnaVIP 3BlockedParent2018-12-03T09:48:44Z
She blew a kiss to a frog! To the freakin' frog! Wtf... It was a perfect opportunity for River to show up or even Amy, Clara, Donna, but no, they went with a frog.... Totally disappointing moment... The rest of the episode was really great though and Jodie was brilliant.