[Merlin]

if (playerenters||created) {
timeout = .5;
}
if (timeout) {
timeout = .5;
if (playery = 49) {
playery--;
this.dir=up;
}
if (this.dir==up) {
playery--;
}
if (playery==11) {
playery++;
this.dir=down;
}
if (this.dir==down) {
playery++;
timeout = .2;
}
}

you need the timeout to make it looped