Don't rely on Gloomy entirely. You'll want to stay there for the majority of the match but Jolly has some good tools as well that shouldn't be ignored. At the very least, you don't want to be helpless whenever you're in Jolly.
Also pay attention to stance shifts and know how to follow through with a combo if you do change. This can be tricky to know what to do every time you switch and from what moves but in time it will come to you.