While it isn't a true combo.. it is very formidable.
There are various ways throughout the combo to reduce the chances of all hits connecting.
First:
Once grabbed, just hold down shield. Heavy characters and fast fallers will land on their feet on the ground very quickly and you will have time to shield before they can up tilt after their downthrow. Wait for the uptilt to connect, then either grab them or roll out.
Second:
Assuming you've been hit with the uptilt, some characters like Dark Pit and Zero Suit can jump out if carefully timed. However, most can't escape, try and DI out anyway.
Third:
They're now Up Airing you. If you're lucky it's on FD where there are no platforms, you'd go up to around 67%. However, if there are platforms, DI away from them, it will prevent Mario from landing on platforms to allow him to perform more up airs.
Fourth:
Assuming you're now at the top of the screen and the last option for Mario is to connect an Up B to attempt to hit you through the roof, try to DI down and away from the Mario, as it will make it more difficult for the Mario to UpB into you, as well as giving you more time to react (preferably with an air dodge or a spacing move like neutral air depending on the character).