I think that the easiest way to learn him is to play him as your first character and learn the game with him.
But it’s too late for that.
I think that his combo execution is not that difficult, but the hardest part is using his attacks and mobility well. With the best flight in the game, he can easily swoop about the screen throwing analyze cubes and such, but he also has 6 frames of not being able to block after jumping. If you want to chicken block with him like everyone else, you have to super jump, which leaves more room for error. Then he has his attacks, which are either slow or with bad hitboxes. He has trouble hitting someone short right in front of him, and he only has two low attacks. His Cr.m puddle, which is really only useful for OTGs and unblockables, and his cr.H, which is slow, but has long range and can be jump-canceled, giving him good high/low pressure that can be seamlessly interwoven. I think that people act like it’s more difficult to mix someone up than it is, because you can easily switch between high and low attacks, and then your throw leads into a combo too.
He also needs the right assists. From what I can tell, the most useful assists for him are, in order:
defensive assist (Lariat, Hulk, Iron Fist to a lesser extent)
A low assist can be helpful, but you shouldn’t change your team composition just to get that. Defensive assist is important when they start to pressure him, because he’s so big and blocking can be overly difficult for him. Lockdown/approach assist like Arthur’s daggers or Dormammu’s Dark Hole (What I’ve been using) helps him get in on them if you are rushing down and hold them in place for his heinous mixups.
And Drones are amazing.
I also think that the way you want to play MODOK is to zone most zoning characters or big characters that have a hard time getting in (Haggar, Hulk), and rush down rushdown characters. MODOK can shut down most zoning characters with his shield and beam, forcing them to come to you. This is usually their weaker point. If they’re a rushdown machine (X-23, Wolverine), you usually want to be on the offensive, as his defensive abilities are weak.
All this in mind, and looking at the characters you play, I would recommend using either MODOK (Psionic Blaster)/Haggar(Double Lariat)/Arthur(Daggers) or Rocket Raccoon (Claymore or pendulum)/MODOK (Psionic Blaster)/Arthur (Daggers)
Probably the second team. The reason why I picked those assists is because Claymore is a good lockdown assist and can be good on the defensive. Pendulum helps cover the screen with crap if that’s your style. Now that Balloon Bomb doesn’t knock down anymore :arazz:, Psionic Blaster is a good beam assist, pretty fast with good durability. Arthur’s Daggers are amazing, especially in Gold Armor. You may want to start Arthur, get him Gold, and tag out to Rocket Raccoon behind an axe or something. Then you have Arthur sitting at anchor spot, ready to be a good anchor and help out the other oddballs with his high durability Gold Dagger assist.
Hope this helps!