Oberon is a cost 100 earth damage dealer with bruiser-like stats and close to tank levels of sturdiness, on top of being able to deliver crippling attacks.
He has about 4 core abilities that can make him a good standout unit on his own:
Purple Dragons Shield gives him an ideal form of barrier available in the game. It also comes with an added bonus of Pierce ATK+ at EX 19 too, making it a strong turn 1 ability that gives him strong defense and offense right away.
Good survivability since he has resistances to single target (Master Ability), Area attack (Purple Dragons Providence), and Slash and Missile from base.
His TMR is also one of a kind, being able to inflict a map-wide debuff that nullifies Haste and reduces all enemy's crit rate for 2 turns. The self ATK+ is the cherry on top.
Damage-wise, he lacks a reliable ranged area attack, but most of them can hit pretty hard. All of his main job attacks also come with some benefit attached to it as well, whether it's chance to inflict Stop/Stun, Pierce/Earth Resist-, or All Element Resist-.