Interdimensional fragments are special collectibles in Treasure Adventure Game. There are 40 in total spread across the game in hidden/hard to reach places or at the end of a small challenge.
Every 10 interdimensional fragments collected unlocks a new upgrade awarded by Elmer at the pawn shop in Danausel. At 10, a heart is unlocked. At 20, the temporal compass. At 30, the torpedo cannon. At 40, the final reward given is 1000 coins.