I recently played a game where a Runaway Carriage was played by the opponent. I was playing as Gideon lvl 60. I gave one of my creatures his Sharp Eyes ability. It blocked the Carriage with its Vigilance, but no damage was done to the Carriage and my creature died. Later in the same game, I gave one of my creatures the Champion ability. It blocked the Carriage with Defender, but no damage was done to the Carriage and my creature died. I never was able to destroy that Carriage.
On a separate game, I had blocked one of these with a creature that naturally had Defender and it killed it on the first block.
I’m not sure whether it is supposed to lose the Prevent Damage ability on the first block and take damage then or on the second block, but there seems to be some inconsistency with what happens to the Prevent Damage ability.