SOLUTION:
1st = Blitzen
2nd = Donder
3rd = Dasher
4th = Cupid
5th = Vixen
6th = Dancer
7th = Prancer
8th = Comet
Logic Sequence:
Clue #1. Vixen = 5th.
Clue #2. Blitzen can’t be 4th or 8th, Donder can’t be 1st or 6th
Clue #3. Dasher = 3rd.
Clue #4. Dancer can’t be 8th or 1st. Cupid can’t be 8th.
Clue #5. Prancer = 7th.
Reviewing clue #2, the only possibility is Blitzen = 1st, Donder = 2nd.
Reviewing clue #4, the only possibility is Dancer = 6th, Cupid = 4th, Comet = 8th.