Terranort's attacks and counters.
Shadow Dash: He keeps making some UNGHAA sound and dashing around.
Counter: Guard this or dash away from it, don't counter hammer.
Slash: Terranorts regular slash that looks exactly how Terra would attack by hitting X.
Counter: Guard+counter hammer
Dark Ars Solum: Series of quick linear slashes that end in him spinning and one final vertical slash.
Counter: Guard+counter hammer
Quick Dark Barrage: A quick volley of dark missles.
Counter: Guard this and make sure you are locked on to him so that the dark missles hit him.
Dark Impulse: He leaps right at you with multiple slashes, covered in darkness, grabs you with a dark claw then sinks into the ground to come up from underneath you.
Counter: Even if you are in the middle of getting slashed to death, keep mashing square and pointing away from him and you will escape the combo. When he sinks into the ground to come towards you, wait until the dark circle is near you, dash TOWARDS him, and you will dash right past him as he comes up underneath you and you'll take no damage.
Dark Barrage: He begins to fire a lot of dark missiles slowly at you, then ends in a burst of dark missles.
Counter: Since you're new to fighting him, just immediately guard and ensure you are locked onto him, this will deflect a bolt at him and it'll end his dark barrage.
Meteor: He'll become invincible and shoot multiple meteors at you after they take some time to rise out of the ground.
Counter: you can guard the meteors, but if you can time a sonic shadow shotlock on him, you can use that to escape the move.
Ultima Cannon: Shoots the big ol' ultima cannon at you.
Counter: Dash away.
Heal: Casts curaga on himself
Counter: heal yourself in this time if you're injured.
If all that doesn't work, watch a video of the fight. It's hard at first but becomes mind-numbingly easy once you beat him the first time.