You are dog (Ralph). Do not let kid (Lee) die.

Left goes left, right goes right, up to jump.

Space to "fire"

If you stand in front of the kid, you will stop him from going forwards for as long as you are there. If you press fire you will make him go in the other direction. The kid will bounce off walls and go back the other way. The kid does not take fall damage, and neither do you.

If you run into the kid from behind, you can push him faster.

Press down to switch places with whatever dog is pushing against, including Lee.

If you stand behind the kid and press space, you'll kick him in the air. This will make him a bit closer to waking up, but can be used to get to high places and avoid bad things.

If you press fire while in the air, you will club whatever's below you. Use this on bouncers and such.

If you walk past a door/skylight from the door side, you'll close it. If you (or Kid) walk past it from the open side, you'll fall in.

If the gap between two things is exactly small enough, Ralph will reach out and become a bridge over them.

If you're on a tightrope/wire, you can jump to get higher. If the kid is on a wire when you jump on it, he'll fall through.

For some reason the rerelease isn't rendering water. If it goes splash, it's water. Dog can swim. Kid cannot.

There are letters that spell "Comic" on each level. You're supposed to collect them.

(This game was published for Comic Relief in something like 1990)

The original game was published in 1993 in aid of Comic Relief. All suggestions that it was a pre-existing game in development that was then hastily rebranded are clearly heretical nonsense. Ahem. All profits from that release went to Comic Relief, though I don't expect Piko are doing that here (Which, to be clear, they're under no obligation to).

You can find the original manual for the game https://archive.org/details/sleepwalker-manual in PDF or more usefully readable forms, like text.

Wikipedia tells me that this was hastily rebranded as "Eek! The Cat!" and released on the SNES too, so there's that. Also that Lenny Henry did the voices, and the credits say Richard Curtis helped "make it funny", so there's someone to blame the thing where if you run off a ledge you fall, but if you stop near the edge you have to sit through a ten second Wile E. Coyote style skit EVERY FREAKING TIME.

I loved this game as a kid when I played the original.