An Interesting Bug : When you're on Level 2, make sure you have a horse when you kill Roy Knife. Once he is dead, walk over his corpse and your horse will be killed. Roy raises from the dead as a sort of indestructible zombie. You can shoot him as much as you like, but he won't die. In this way you can play until you get tired of it.
Secrect Character : If the total of inserted credit (NOT current credit) is a multiple of 16 (16, 32, 48...), the secret character 'Aka-jirou' (Red-dragonfly) appears and you can get 10000 pts when you kill it.
The number of dragonflies at one time is changed by current total inserted credit, for example : 64 credits = 4 dragonflies, 128 credits = 8 dragonfiles.
But in case of 256 credits, 50 dragonflies appear instead of 16!