@ShadowOne333 mgba should be back
Yep it's back on the nightlies

Both in the full package and individual formats. Thanks!
One more thing,
@Radius4.
I also noticed there is a new mame2003-plus core.
Apparently this one is a further modified mame2003 core which adds some stuff to make some games run better and/or compatible with the 2003 emulator. But, some odd reason, I cannot get RetroArch to detect this core to boot the zip files in which the games are stored in.
If I try to boot via Load Content, RetroArch doesn't detect this core to boot the ROMs with.
Also, I changed my MAME.lpl playlist to run the ROMs using mame2003-plus_libretro.rpx instead of the already existing mame2003_libretro.rpx core, and now the playlist doesn't appear at all in the lists. They do appear if I put back the original core in the LPL file.
Just thought about letting you know, perhaps this one hasn't been added in full in RA yet.