7 long Skewers
An elastic band
Build the base
You will need three marshmallows and three skewers (be careful of the sharp ends)
Use them to form a triangle
Use another three skewers and another marshmallow to make a pyramid shape.
Take your last skewer to make the arm to propel your marshmallow.
Use sticky tape a spoon to the skewer and stick it in one of the three base corners.
Wrap the elastic band around the top marshmallow and the spoon and you are ready to launch your marshmallows!
Be gentle with it at first, after a day your marshmallows will harden and be more stable but hold the base and take it easy - if it breaks remember you know how to fix it and engineering can be tricky - practice is the only thing that will help you improve these skills.
Can you make any improvements - perhaps use a glue gun if you have one available to you instead of marshmallows...