Well, I'm using Yosniper's Engine for my new fangame too, and I think I know the problem : he made the gravity weak when the kid is underwater, but the maximum fall speed is still 8.
Here's what I did to solve it.
Find the object player, and look for 'End step'(Is it says so in English? because I'm not using English version so I don't know)
anyway, next you find the 'else if place_meeting(x, y, water)'
there, the code says :
else if place_meeting(x, y, water) {gravity = 0.25;}
if you find it, add this to there:
if vspeed>2{vspeed = 2;}
so the result will be this(this is exact same code with mine):
else if place_meeting(x, y, water) {gravity = 0.25;if vspeed>2{vspeed = 2;}}
this may make the kid fall slower than before underwater(I didn't used the underwater gimmick yet so you'll need to test it yourself, and if you think 2 is too slow, you can change the number). of course, you can modify the 'maxFallSpeed' variable, but I didn't want to because I thought what I did was the more simple way.
