Toliet you have to use both stances, sometimes it's better to stay in jolly then in gloomy because you lose heath in gloomy.
Just telling you now, tira's not an easy character to learn. She was awkward for me when i first started
They're not the hardest characters tbh, brad wong is just a nightmare to learn in this game and the closest character to that difficulty that i've learned is zafina from tekken
still as long as you master one stance you should be fine