Popular rogue-lite 2D platformer Skul: The Hero Slayer recently got a big upgrade with The Dark Mirror and it looks pretty great.
For those who want more of a challenge, this free update is for you. The Dark Mirror game mode is like a fresh dedicated hard mode for the game, adding in more powerful enemies and threats. However, the developer explained "We would like to say the Dark Mirror update is not just a hard mode that has increased the health and damage of the enemies. It is more of a new DLC, which includes a new story and content. We highly recommend that players personally experience the DLC's full content rather than experiencing it through written texts and images. For these reasons, further details related to the Dark Mirror will be included in the Dev Blog."
While it does offer Native Linux support, I use the word "support" quite loosely here. It has a Linux version, but the developers don't actually seem to test it. The current version still gives you a black screen instead of an actual intro and main menu. It's an easy fix, setting "-force-vulkan" as a launch option for the game, something I told the developer about quite a few times but they haven't bothered to fix it.
Apart from the above, the game is a lot of fun though, swapping heads to gain different abilities is a fun game mechanic.