INTERACTIVE BACKGROUNDS

SMBX offers all sorts of background objects you can use to decorate your stages, but some of them have unique attributes that aren't entirely obvious. This article covers everything from the self-evident to the obscure.

We'll knock out the simple stuff first.



These objects all have one thing in common: they appear in the foreground. This makes them useful for custom sprites if you want something to appear in front of NPCs instead of behind them. Also of note is that the sideways version of the propeller is NOT foreground. Lastly, quicksand has a background variant as well.



The keyhole exits the level when you touch it while carrying a key. That's nothing too special. However, the doors in this picture are all animated. If the player enters a door warp while touching one of these doors, it will play its open/close animation. They will do this even if they're on a hidden layer. That can cause weird visual problems if you're not careful. This is because the open/close animation is an effect graphic. If you were to change the sprites of these doors, you'd have to change their effect as well.



Water tiles, specifically water surfaces, have a special property that isn't entirely obvious. If the player or an NPC falls into a water block when near one of these tiles, they will generate a splash effect at a set height above them. Likewise, a splash is generated when something pops out of a water block nearby. This is significant for two reasons.

First, the height you place your water block is important in regard to these tiles. If the block is too high or low, a splash won't be generated. Sometimes you can have the height such that a splash is made going in, but no splash occurs when going out. You have to test and make sure it looks right where you have it placed, though setting it in line with the water's surface is usually safe.

The second reason this matters is in regards to custom graphics. If you're using a custom water surface, you should choose a resprite based on the water's height. Since the splash appears at a set distance, using a water sprite that's too high or low won't look proper.

Like the doors in the previous example, water surfaces will still generate splashes even if they're on a hidden layer. However, they only generate splashes if there's an actual water block present.

The only water surface tile that doesn't generate a splash is the SMB3 waterfall top. Non-surface tiles don't generate splashes either.



The rail lift tiles are fairly self-explanatory. NPC platforms and the Grinder NPC follow the tracks wherever the lines guide them. What you may not know is that the turning end pieces do not merely function as caps. They actually reverse the momentum of rail lift NPCs that touch them. So, if a Grinder were to fall directly onto an end piece, it would bounce back exactly the way it came, whether a rail lift line was there or not. This can create some interesting hazards.

The same is true for NPC platforms, but you have to be careful with these. The platforms stay active while off-screen instead of despawning, so if one is caught in midair off-screen for too long, it can pick up absurd amounts of momentum. A bouncing platform could end up rocketing far off the top of the screen!



The fence is the last of the interactive backgrounds. The obvious aspect of these tiles is that you can climb on them. However, they're also connected to a very unfortunate glitch.

In SMBX, when Mario is standing on a moving layer, the game assigns separate momentum variables to him. It's what allows him to ride solid objects without getting accidentally wall crushed. When a layer Mario is riding stops, these variables are set back to zero. But, if Mario jumps off the moving layer before it halts completely, the variables retain their values.

This only becomes a problem when this fence is involved. When Mario climbs on this fence, he will be dragged in whatever direction the last moving solid had him going. This causes very strange behavior and can make Mario lose his grip on the fence entirely. It's best to avoid having these fences in stages with moving parts. Incidentally, climbable NPCs are unaffected by this glitch.

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So now you know the truth behind these seemingly static tiles. Arm yourself with knowledge, and make your levels better for it!