He was one of those guys that got on top of you and almost automatically won from there, his grappling was ridiculously legit, he competed in ADCC and obliterated everyone he faced in there, no one even scored a point against him
In the beggining of his career at 2-0 Arona fought Fedor at Rings: King of Kings 2000
As you can see, Arona completely dominated Fedor in the grappling department, and Fedor is considered a grappling god, Arona took his back, mounted him, and he only lost the mount because he went for those foolish arm attacks (judges on your ass screaming action doesnt help).
Arona went on to dish a ridiculous ammount of destruction against Sakuraba and compete against many others, he outpointed wanderlei to a decision the first time (and probably the second as well)
He had some badluck, fighting prime roided wand + shogun in one night is thought business
The rampage slam didnt KO him, an illegal headbutt between the slam did
Lots of luck arona, wish you well!