Lost Marbles are something you can find in the different zones you’ll visit during your adventure through Tiny Tina’s Wonderland. Here you’ll be navigated to the Lost Marbles which are scattered around Weepwild Dankness.
Lost Marble Location #1 - The Corrupted Heart
Head to The Corrupted Heart Fast Travel and follow the path down until you see a set of stairs, then when you get to the top, look to the left to find some vines with a chest in front of it. Walk along the vine to reach the upper area and you’ll find the Lost Marble near a crate with some candles.
Lost Marble Location #2 - Busted-Ass Ruins
Head to the Busted-Ass Fast Travel and then follow the path down to the southeast and you’ll come across a watchtower. Use the platform to the left of it to climb up and smash the Lost Marble.