I tend to do pretty good with Pyroak, in addition to his great defensive game, he is incredible at applying constant pressure, thanks in large part to his slow moving Energy Ball. You add to that solid normals and the threat of Woodhammer/Flamethrower for jumpers and you have a character that really excels at locking down and limiting your opponent's options.
My favorite string after they block a jump in his cr.weak x 2, cr/st. med, followed either by an Energy Ball so I can dash forward and continue the pressure or a Woodhammer which, if they block, will keep you safe, or if theyre blocking low (and they'll have to if they don't want to be hit by cr.wk) will smash them into the ground.
Slow Energy Ball is simply fantastic. It's very tough to jump over, and Oak loves people jumping in at him anyway. Most players will be cautious when they have a ball floating towards them which means you're safe to dash or jump in without too much fear.
Oak also does surprisingly well in the air. j.wk, the headbutt, has great priority and you can usually follow it up with a Flamethrower if you hit them at the peak of your jump. j.med has really good range and functions well as a jump in to. j.sg is quite slow, but deals good damage and can cross up, but requires you to be rather close as his jump arc isnt the most impressive.
His real damage dealer is the Uproot set up however. There are instances when they'll be hit with an EBall and you can dash in and Uproot before they can recover.
Following this, you CAN Flamethrower for easy damage. But if you're feeling up to it, you can get a lot more damage with a j.wk followed by a juggle of your choice. I think I've seen TGM do something to the effect of Uproot>j.wk>st.wk>st.md>eball>flamethrower....or something equally impressive. If you have Solarbeam, you can replace the Flamethrower with it for even more damage.
Ungulateman is right though. Your meter is going to be spent on Ember. It can be good if you're anticipating your opponent to do something (catches Fidgit trying to Earth Power all the time for a beneficial trade at worst) but it's especially great for punishing. If you block an attack, and they're too out of range for an Uproot: st.sg > Ember will do massive damage for a simple one two combo.
Pyroak is a neglected character these days, which is too bad considering how powerful he is. One of the least mobile characters in the game, but also one of the best at preventing others from going where they want with his great pressure game.