For a handheld thats been gone for years heres a first time rom hack for the Atari Lynx:

Switchblade II is a platform game, originally released on the Commodore Amiga and Atari ST, with a cut-down port for the Atari Lynx, and now thereís a hack for it. The hack itself is quite simple - giving you the ability to continue from where you died, and giving you only one life at the start as a form of balance - but itís notable for two reasons.
Itís the very first hack for the Atari Lynx on this site, and secondly, it was done without any debugging tools, save a memory viewer. The author identified the assembly instructions due to their similarity to other systems like the NES, and made educated guesses to achieve the desired effect.
Itís a game that many wonít be aware of, but now that this hack makes it somewhat easier to play, why not give it a try?