If you programed your own custom engine, you'd know exactly why he's not able to walk up stairs. For example, maybe each step is being detected as a wall, because your wall sensors are too low. You can fix this by raising up the wall sensors and then shortening them so they don't go over his head. Then you may have to tweak the engine a little more if you haven't done so already, with a fastloop, anti-sink setup. Now your player will ignore the stairs rather then walk into them like walls, and your anti-sink setup will kick him up each stair. If you want to make this process smoother, you could also just make invisible objects between each stair that you can only detect when you're moving, that way when you walk up and down them, you're transitioning from stair to stair, but when you stand still, you still stand flat on the stairs.
Of course, none of this matters if you're using the default movement, and considering the platform engine is by far the worst of all the default movement engines, I strong recommend you start working on a custom engine.
Sounds like it doesn't support slopes to me. Get slopes working=get steps working (depending on how you're doing them, old Castlevania style or new etc).
Originally Posted by Peblo I recommend the PMO extension. Although custom movement is better, I dunno if you're at that stage. Much easier, and usually enough.