SPG:Underwater
From Sonic Retro
Note: Research gathered from Sonic the Hedgehog (16-bit), but it is highly likely that it holds true for Sonic CD, Sonic 2, Sonic 3, and Sonic & Knuckles.
When Sonic is underwater he moves much more slowly, but otherwise his physics are largely the same. This is achieved mostly by halving the pertinent variables, but some, like gravity and initial jump velocity, are not exactly half.
Contents
Variables
Acceleration
Acceleration has a value half that of normal: 0.0234375.
Deceleration
Deceleration has a value half that of normal: 0.25.
Rolling deceleration is remains unchanged.
Friction
Friction has a value half that of normal: 0.0234375.
Rolling friction has a value of 0.01171875.
Top Speed
Sonic's top running speed is 3, half that of normal.
Air Acceleration
Sonic's air acceleration behaves the same way, but has a value of 0.046875, half that of normal.
Gravity
Gravity is 0.0625, instead. This causes Sonic to fall much more slowly.
Jump Velocity
Inital jump velocity is equal to -3.5, and release velocity is equal to -2.
Bubbles
When Sonic gets a bubble underwater, his X speed and Y speed are both set to 0.
Entry & Exit
When Sonic hits the water, his Y speed is multiplied by 0.25 (this occurs after gravity is added). Basically, whatever his Y speed is, it's cut to a quarter of itself. Conversely, when Sonic leaps out of the water, his Y speed is doubled (after water gravity has been added), so that he begins moving faster now that water no longer impedes his movement.
Drowning
When Sonic drowns, his X speed and Y speed are both set to 0, and the water gravity remains normal.
Speed Shoes
When in possession of Speed Shoes, but also underwater, the underwater variables take over, effectively nullifying the Speed Shoes altogether. No calculations, such as multiplying by 0.5, take place.