I've figured out how to make a death controller, and a jump & gravity controller, but wall collision I have no idea how to make. The color for the ground is #00ff00. Any help is appreciated!

if you have an “X speed” variable you can do…

define a new block (Run without screen refresh)
change y by (3) (to move off the ground)
if <touching [ground sprite]?> then
change x by (X speed)
end

oops, what I meant was

change y by (3)

to move off the ground


and also, you can put

when green flag clicked
forever
a new block
end