There are a few version differences in this game, see https://tcrf.net/Daffy_Duck:_The_Marvin_Missions_%28Game_Boy%29#Revisional_Changes This page is in need of an update though.

1. Plain gameboy version (EU, US)

• no background graphic on the title screen
• Only one shot will hit per frame. Two shots can't hit at the same time; the 2nd shot will be ignored.
• No health bug
• Out of bounds warp glitch in level 1 doesn't work
• All enemies are present

2. Super gameboy version (EU, US?)

• Background graphic on the title screen is present
• Multiple shots can register
• Health bug is present (walk left and jump right frame-perfectly to activate, gives you about 64 units more health and makes the health display glitch so you can tell if you got it)
• Out of bounds warp glitch in level 1 works (this is the version the glitched TAS uses)
• Some enemies are missing. See the tcrf page linked above.

3. Super gameboy version (JP)

• Background graphic is present
• Multiple shots = Not known if they can register, needs testing
• Health bug is present
• Out of bounds warp glitch = needs testing
• All enemies present

The things that influence speedruns the most is the health bug and the additional enemies. So the best version to use is 2) SGB for EU and US.