The final boss fight comes in two sections. The first section is straightforward, just avoid his attacks and get your correct move in just before he disappears.
After he turns into a giant dragon creature learn his pre-attack moves/sounds. Duck for the flame from his mouth, move to the centre of the screen for the vertical and diagonal fire streams, use shield to protect against the blue projectiles from his mouth, jump (but not too early) to avoid his fist pound.
The easiest way to beat him I found is to remove his shield and then stand close to his arm and just use Olmec's Headbutt repeatedly (pressing O). Retreat/jump/shield for his attacks which will give your stamina time to recover then move in (hopefully before his shield goes back up) and headbutt away.
If you do this without catching and throwing any of the falling projectiles at him you will also get Up Close And Personal.