The Gigant! Mind you it was initially designed as a glider.
But of course there were several transport-carrying gliders from the allied side.
The Horsa?
As a sidenote what would have been the heaviest aircraft of WW2 to take off by it's own power. My money is on the B29, the Lancie being the runner up, but again some may have been heavier. Ok - in sqn service?