Lineguard

He runs. You draw. Keep him alive. A little ink ninja runs across a painted world on his own, and you can't steer him. All you can do is draw. Every line you sketch is solid for a few seconds: put one in front of an arrow and it stops, angle it right and the arrow flies straight back at the archer who fired it. Draw under his feet to bridge thorns and pits, or draw a ramp and send him flying. Time slows while your pen is down, and you only carry a few drops of ink, so every stroke counts.