Simon, Slave of kThung is a little different than most Demigods, in that he is not so much the main character, compared to the powerful Demon who controls him. He starts with the ability "Summon kThung" that summons a powerful Demonic Creature from the Abyss, who has enslaved this 'Demigod'. kThung is essentially immortal, but doing damage to him will cause him to become unsummoned, and killing Simon will of course sever his ties with this Plane of Existence. So yeah, he acts just like a normal minion in all these ways.
The difference is that most of Simon's abilities increase the power of kThung, and not himself. The strength of Simon, Slave of kThung is that he essentially has kThung do most of the hands on work, while he sits fairly far away and doesn't intervene. As he levels, the radius in which Simon can resummon kThung gets larger, allowing him to surprise opponents by getting this hard hitting Demon in close with them. As Simon Levels it starts off with him generally just boosting up kThung... but eventually it becomes harder to tell who is the master, and who is the servant...
Summon kThung: Radius of 15, casting the spell while kThung is already out will replenish all of kThung's health, and move him to a new location. 45 Second Cooldown
Improved Summoning: Increases the Radius in which kThung can be summoned by 5, and decreases the cooldown to resummon by 5. There are 4 Levels of this skill.
Hellgate: (Requires 4 levels in Improved Summoning) When kThung is summoned, a little bit of the Abyss he comes from comes with him, dealing 500 damage to everything in a 10 radius around the point he is summoned.
Demonic Pact: Allows kThung to retain more of his strength while in this plane. Increases Attack Speed by 10/15/20%, and gives kThung the ability to damage the mana of his targetting, giving him a 15% chance to damage 100/200/300 mana on the target.
Sacrifice the Weak: Funnels health from Simon to increase the strength of kThung. Lasts for 10 seconds, and has a range of 10. Simon takes 20/30/40 damage per second, and kThung's attacks have a 10/20/30% chance to crit for 2x damage. Simon cannot break the effect.
Portal Control: Target portal you control spawns an additional 1/2/3/4 imp creeps per wave for the next 2 waves. They give no experience or gold, and do AoE ranged damage.
Portal Master: (Requires 4 ranks in Portal Control) When you use Portal Control on a portal, it spawns its next wave of creeps immediately.
Blood Sacrifice: When kThung is summoned, Simon loses 100/200/300 health, but kThung gains 300/600/900 more hit points and 400/800/1200 more armor.
Demonology: Simon gains 5/10/15/20% of the damage he deals as mana. (Does not apply to damage from his minions).
Demoninance(Requires 3 levels in Demonic Pact): Allows Simon to Transition to a Demonic Form. To do this, kThung must be in play. kThung dissappears, and Simon moves to whatever position kThung used to be in. While in this form effects which normally apply to kThung now apply to Simon. These include Blood Sacrifice, Demonic Pacts, and he can target himself with 'sacrifice the weak'. Activating the ability triggers the Hellgate effect if it exists. Summoning kThung ends the effect, and puts it into cooldown for 30 seconds.
So how does all work together? Simon basically plays a Demon general who likes to sit in the back and let his friends do the work... until level 10 where he has the first chance to try out Demoninance, and become the demon himself. His portal Master skill can allow him to be an extremely effective portal capper, as he can summon additional forces to help him hold the portal, in the form of the formiddable Imps.
He is by far the frailest DG around though, as many of his abilities actually cost him health in addition to mana. He will also start with minimal HP and Armor. And while he likes to not get in close, he still will want to be in a lane to get experience, so his health vulnerability is noticeable. Even if kThung may be a fairly powerful guy, none of that helps if Simon get's ganked.
Once Simon gets to level 10 though, things to crazy. He can potentially teleport a decent range by using Demoninance and Improved Summoning... with an explosive burst no less. He can control waves of creeps to help siege a tower, and can start tanking if he has a lot of points in Blood Sacrifice. The idea is definitely that Simon is a late game DG.