Aerial Movement Mechanics: The intricacies of the Smash Bros engine

Yesterday we spent a lot of time talking about movement options, so before we get to hard programming the engine I want to talk about some parts of the Smash Bros. engine—specifically, the huge degree of hidden movement options that make the games not only unique but, more importantly, intuitive and friendly to casual and competitive players.  (also I apologize in advance about the quality of the video and the lack of gifs, I was having trouble making them work and figured the writeup is more important)

As I'm too lazy to write a quality intro paragraph, I'll cut to the good stuff.  Many Smash Bros players know about the short hop (done by pressing jump and quickly releasing) and Melee players know about dash dancing (rapidly dashing back and forth without entering turnaround animation), but some of the most interesting and impactful mechanics are far simpler than either of these—things like air speed and character gravity are what give characters their FEEL.  For example, Melee Captain Falcon is well-known to be a very fast but hard-to-control character.  WHY?  A few factors: Maximum Air Speed, Character Gravity, Fall Speed, Fast Fall Speed, Aerial Acceleration, and Short Hop Height.  While Short Hop Height is pretty self-explanatory, the others are both barely visible but very influential.

Maximum Air Speed is simply the greatest horizontal speed at which a given character can move while not in hitstun.  Melee Captain Falcon has a high air speed, which part of what allows him to run, jump, and Falcon Punch an opponent on the other side of Final Destination.  However, it's also very easy to jump too far and jump off the side of the stage, resulting in a dramatic but very silly self-destruct. (guilty) As Captain Falcon, once you're in the air, it's hard to stop.

Compare that to Jigglypuff or Wario—both characters can move quite quickly in the air (high Max Air Speed), but unlike Falcon, they can easily switch directions mid-air. (Feel free to try it—jump away from your opponent as Jigglypuff, then hold back towards them and attack) This is due to a separate variable I'll call Aerial Acceleration, and the greater it is, the more control you'll have over your character in the air.  Characters with greater Aerial Acceleration can also dodge in and out of danger in the air; this is notably a core part of Jigglypuff's entire strategy.  Captain Falcon, on the other hand, has a low Aerial Acceleration (try the Jigglypuff maneuver with Falcon—it won't work), which both makes him difficult for newer players to control and limits his options while airborne.  Both Max Air Speed and Aerial Acceleration make an impact on a character's feel and strategy.

(For the physics people out there, Aerial Acceleration vs. Max Air Speed is acceleration vs. max velocity, considering only the x-components)

Let's move on to Gravity, Fall Speed, and Fast Fall Speed—three similar-sounding concepts that set the tone of the entire game.

First off, Gravity is very similar to real life gravity, except it varies for each character—the higher one's Gravity value, the greater one's constant downward acceleration.  Gravity is applied at all times on combatants, thus affecting max jump height, recoveries, and even resistance to dying off the top of the screen.

Fall Speed, on the other hand, is the maximum downward velocity a character can achieve when unaffected by outside forces—essentially, terminal velocity.  While it's true that Fall Speed and Gravity tend to either both be high or both be low on a given character (thus fast fallers vs. floaties) a difference in values can have an impact on a character's playstyle or recovery—for example, Bowser has a high Gravity but a low Fall Speed, which helps him float back to the stage when knocked off. (For the physics people out there, Gravity vs. Fall Speed is essentially acceleration vs. max velocity, while only considering the y-components)

Finally, Fast Fall Speed is extremely similar to Fall Speed, with the main difference being its user activation.  After jumping, the player can input down on the control stick to instantly achieve a higher-than-normal downward speed, which again, varies by character. (I specify after jumping as a character who has just been launched cannot fast fall!) This allows advanced techniques like SHFFL'ing (or just SHFF in Brawl/Sm4sh) and is a core part of many characters' gameplay.  It also, again, affects the feel of some characters, like King Dedede, who has lower gravity, to achieve a "floaty" feel, but has an extremely high Fast Fall Speed, to give him a "fat penguin" feel.

All these little values add up to give the Smash Bros. series not only unique-feeling characters, but serious competitive depth—a universal plus, if a bit taxing on the programmers and balance testers.  In my opinion, they should not be overlooked without serious consideration.

Now, for anyone who isn't bored, there's one more thing I'd like to cover, specifically about Soku and other fighting games vs. Smash Bros (engine-wise), which (IMO) greatly contributes to the Smash Bros "feel".

Soku jumps vs. Smash Bros jumps—an intuitive feeling
When I first played Soku, jumping felt weird to me.  The only fighting games I'd ever played previously were Smash Bros titles, so I was used to the noob-friendly controls Smash Bros provided—namely, Aerial Acceleration.  In Soku (and I believe most other fighting games), I can jump in 3 directions—forward, straight up, and back—but, once airborne, I CANNOT CHANGE MY AERIAL MOMENTUM BY HOLDING LEFT OR RIGHT.  This is a huge distinction, on both a casual and competitive level—casually, I can't simply hold left and gain leftward velocity; competitively, it makes every jump much more of a commitment with much less room for error, as I can't simply hold back and begin to fall back—I need to either attack or burn another jump, or risk being swatted out of the air.  Smash Bros is very intuitive in that one can simply hold left to go left, even in the air.  While I eventually adapted to Soku's more traditional jumping system, the Smash Bros jumping system has a platformer's intuitive feel that makes it easier for anyone to get into the game.

Ultimately, I think the Smash Bros engine has lots of little-known quirks and values that add immense potential for characterization, competitive depth, and an intuitive feel.  These aspects of the games should not be excluded without major discussion.

TL;DR Smash Bros engine is complex but feels fun.  It's successful for a reason.

Thanks for writing that. I've been trying to take into account details like that in my character writeups, but it seems there are more properties I should think about. I already kinda knew about them, I guess, but never thought of writing stuff down in that level of detail.

You also made me figure out how to give Reimu the aerial mobility I want for her without giving her extra jumps. All in that aerial acceleration, baby!