The Dragon Curve created using GBDK's 2D plotter APIs. I know it's not entirely optimal code.

dragon_curve.c

// Dragon Curve for Gameboy, using GBDK
// By Will Kirkby 2013
//
// Ported from Eelke Schipper's http://www.khanacademy.org/cs/dragon-curve/1414142328
//
// Use the up and down buttons to
// increase or decrease the number of folds.
//
// (1 << n) is used in place of pow(2, n) for speed purposes.

#include <gb/gb.h>
#include <gb/drawing.h>

// Is direction is the nth fold left?
// could put this in a table to optimise, considering the limited fold range we've got....
UINT8 isLeft(UINT16 n) {
    return (((n & -n) << 1) & n) != 0;
}

void drawCurve(UINT8 folds, UINT8 clear) {
    UINT16 segmentCount, i;
	INT8 segmentSize;
	INT8 segmentX, segmentY, nsegmentX, nsegmentY;
	INT8 x, y, dx, dy, newX, newY;
	UINT8 dir;

    // The number of segments we draw
	segmentCount = 1 << folds;
	segmentSize = 80 / (1 << ((folds + 1) >> 1));
	// The direction of the segments
	segmentX = segmentSize;
	segmentY = segmentSize;
	if ((folds & 1) == 0)
		segmentX = 0;
		
	nsegmentX = -segmentX;
	nsegmentY = -segmentY;
	
	// Clear the previous render.
	if (clear) {
		color(WHITE, WHITE, SOLID);
		box(0, 0, 159, 143, M_FILL);
	}
	
	color(BLACK, WHITE, SOLID);
	
	gotogxy(0, 0);
	gprintf("Folds: %d", folds);
	gotogxy(0, 1);
	gprintf("Segments: ");
	gprintn(segmentCount, 10, UNSIGNED);	// just run with it.... hacky code for a hacky library.
	
		
	// Start point
	x = 40;
	y = 72;
	
	// Direction should be 0, 1, 2 or 3.
	dir = 0;
	dir = ((folds - 1) >> 1) & 0x03;
	if (dir != 0)
		dir = 4 - dir;
	
	i = 0;
	// yeah... let's use labels to simulate a loop. apparently GBDK doesn't like loops with INT16s.
	drawfold:
		i++;
		switch (dir) {	// could probably optimise this too... table lookup anyone?
			case 0:
				dx =  segmentX;
				dy =  segmentY;
				break;
			case 1:
				dx =  segmentY;
				dy = nsegmentX;
				break;
			case 2:
				dx = nsegmentX;
				dy = nsegmentY;
				break;
			case 3:
				dx = nsegmentY;
				dy =  segmentX;
				break;
	    }
			
		newX = x + dx;
		newY = y + dy;
		line(x, y, newX, newY);
		x = newX;
		y = newY;
		
	    // Turn dir, lots of optimisation here.
		if (isLeft(i))
			dir--;
		else
			dir++;
		dir &= 0x03;	// same as dir %= 4;
		
		if (i == segmentCount)
			goto afterloop;		// break
			
		goto drawfold;	// loop back
		
	afterloop:
	return;	// apparently I need a statement between the label and the closing brace.
}

void main() {
	UINT8 folds, btns, btns_old, key_was_pressed;
	
	folds = 1;
	btns = 0;
	btns_old = 0;
	key_was_pressed = 0;
	
	drawCurve(folds, 0);
	
	// game loop
	loop:
		wait_vbl_done();
		// Input
		btns = joypad();
		if ((btns & J_UP) && !(btns_old & J_UP)) {
			if (folds != 7) {
				key_was_pressed = 1;
				folds++;
			}
		}
		else if ((btns & J_DOWN) && !(btns_old & J_DOWN)) {
			if (folds != 1) {
				key_was_pressed = 1;
				folds--;
			}
		}
		if (key_was_pressed) {
			drawCurve(folds, 1);
			key_was_pressed = 0;
		}
		btns_old = btns;
	goto loop;
}