I got a little annoyed with left-right, up-down or up-down-left-right enemy movements and tried to use checkpoints, which is rather difficult for me withing the scope of the AGD.
Having made a few lame attempts - even global vars aren't enough and handy - I though how, say, SEUD, could do those tricky moves. Perhaps it's a PATH system -- a set of (smoothed) checkpoints or predefined behavior pattern.
In the AGD it's possible to modify the behavior (via scripts), but it requires either some formulae or hard-coded subs. I think that eight PATHs, if have some up to eight points, both smoothed and not, (let alone scalable) would do nicely, provided it's not too resources expensive.
well I don't know if this can be of any help, but in "donkey kong reloaded" I had my barrels (or turtles or skeleton gorillas) as left-right patrolling enemies to which i added " if cangodown fall endif" and also i put a deadly block in the bottom of the screen so when they would hit it the would be removed and spawned again at the top of the screen in a random y position...that is quite simple to realize and i tink gives a nice effect and some impredicatbility of behaviour...hope it helps Gab