I'm planning to use the Swooper Bat sprite for a bit of a different purpose, in which I have it placed on the ground and have it going upward instead of downward like it normally does.
I managed to pull this off by changing the byte at $0388FC to FF, causing it to descend. The only issue, however, is that it continues to ascend to the top of the screen without stopping. I tried editing other bytes around it and couldn't get the result I wanted without very buggy side effects. Is there a way to have it properly ascend but also have it stop after a bit?
You also need to change the direction in which the Y speed changes over time. Try changing $0388FC to E0 (same speed as the original but in the opposite direction), and also changing $03890F to F6 (INC, rather than DEC).