wait, is that rare?

0_0
so does a juju now has it?

it isn't too difficult to convert.

why do you have the whitespace on the right, anyways, can't you just use horizontal, grab the next two columns of pixels and draw them?

wait, so do you have separate frames for every look the background can take, then?
if so, then that would be very fast, absolutely massive, and not require horizontal at all. if not, then i don't understand...

judging from the fact that you are shifting the buffer before updating the screen, i'm guessing you are, indeed, drawing the entire background every frame rather than just the rightmost column of pixels. if you were to swap drawing the entire background in monochrome for drawing only the rightmost column it would mean a change from 96 sprites for monochrome to 32 for greyscale.

if you're doing it that way already, though, then my mistake

if you are basing your enemies on those of the first zelda game, there doesn't have to be any diagonal motion at all except for zora projectiles, which can move in 16 directions and can't change direction once they start. other games are a bit more complicated, though. here are a few quick examples of how enemies move:

for collisions, just use (<pixel position>+<amount of pixels the screen has scrolled since the last tile change>)/<tile size>+<tile offset to the top/left most tile being displayed on the screen> to find the tile a specific pixel is inside. that means that, in order to find the tile above/to the left of your character you would make pixel position the player's position minus one, and to find below/to the right of it would be player position+player size+1

you can do enemy collisions the same way, storing the player's position somewhere and then checking the enemy position against it. it would use their absolute pixel positions (x,y on the screen+tile offset*tile size), though, and would have to use regions, though, so the check for a contact between the player and an enemy would be:
(player position < enemy position < player position + player size) or (player position < enemy position + enemy size < player position +player size), where the positions are the top/leftmost pixel in the sprite. you don't need to worry about having any <= in there unless you make enemies that move in increments larger than enemy increment+player increment, because link gets knocked back by enemies, so they will never be exactly on top of him.

zelda AI should be simple, as they're mostly just moving in straight lines and turning at random intervals or moving towards the player. bosses may be more difficult, though.

just make bullets a special type of enemy that moves faster and deal with them the same way.