what this code is supposed to do is pull you down 400 milliseconds after jumping into the air but instead it wont do that and will just multiply your speed on the ground.
if (PlayerUtil.isInLiquid() || mc.gameSettings.keyBindJump.isKeyDown()) return;
if (MovementUtil.isMoving()) {
if (mc.thePlayer.onGround) {
MovementUtil.setSpeed(MovementUtil.getAllowedHorizontalDistance() - Math.random() / 100.0D);
mc.thePlayer.jump();
if (Math.abs(this.lastAngle - Math.atan(mc.thePlayer.motionX / mc.thePlayer.motionZ) * 57.29577951308232D) > 20.0D) {
MovementUtil.setSpeed((float) (0.434784145f + (0.0232600284172 * (EffectUtil.getAmplifier(Potion.moveSpeed) - 1)) + (.044 * mc.thePlayer.movementInput.moveForward)));
if (timer.hasTimePassed(400))
mc.thePlayer.motionY = -10;
timer.reset();```