They only have to change their name if it’s trademarked, which Pixel Dungeon isn’t.

There are in fact over 300 versions/mods (not including all the different revisions of each) of the original Pixel Dungeon, Pixel Dungeons for various OS’s, and serveral games that use the same title although they have no relationship to this Pixel Dungeon. When Doyla/Watabou released the source code for Pixel Dungeon to the public, there was no copyright, registration, or trademark involved, just a GPL. I recently brought this version you mention to the attention of this community. As it is not a working game as yet, or not available to the public for testing, not much can be said. The game has some elements of Pixel Dungeon 3D and other games. In fairness, it is not being presented as Shattered Pixel Dungeon, and it may be that the PD source was used. It may also be a clone. A PD fan inspired original game. Without further details one can only speculate. Reguardless, if they want to use the PD name, there is no legal recourse against it. Fan’s of PD could rally to boycott as they have in the past, but to what end or extent? Should we attack all game clones? Should we go after all PD mods? Should the fans of original non-graphical Rogue-likes join in the battle to take down all graphical Rogue-likes. It’s a slippery slope to start saying lets take legal action against open source software - you may as well be Micro$soft.