DC: Justice League Legion is currently a work in process.
Heroes by Class
Differences to Avengers Alliance
The most extreme difference is that there will be no playable agent-like character.
Reason for that being that when MAA first got launched, the only non-agent related form of customization in the game was stat increasing isos and the ability to change the class of a specific hero via alternate uniforms. Since the game has evolved to a point that it now has empowered and augmented isos, there is little need for a character such as the agent to exist.
You'll have to name and customize a Watchtower employee at the start of the game, but they will never be used in combat and is solely for identification.
Besides, no one ever started playing Avengers Alliance so that they could be a personality-less S.H.E.I.L.D. agent.
The level you are able to reach is infinite.
At levels 161 - 300 the amount of XP needed to level up remains static at 4000 XP. At levels 300 and beyond, the number of Experience Points needed to level up remains static at 16000 XP.
Since you don't have the agent-like character in combat, you'll character will receive XP from winning mission battles, regardless of who remains in battle.
DC: Justice League Legion will start with empowered and augmented isos available, but only the original starting isos.
You'll have the ability to raise your heroes to level 15. The Level 15 Multi-Action Abilities will stay the same aside from two differences. Removing the starting cooldown for tacticians and reducing generalist's Long Haul cooldown from 4 to 2.
Got rid of the relentless passive (or at least in the process of) that bosses tended to have.
To further make villains more similar to the heroes they fight, all enemies' actions cost stamina thus enabling them to also recharge. Villain's stamina costs are half of those of an average hero to factor out on them still taking two turns each round.
The challenge mode in DC: Justice League Legion will be much more difficult than in MAA. In challenge mode, all enemies will use Multi-Action class abilities, identical to the ones heroes obtain when reaching level 15.
Ignoring all the fatuous changes MAA did to counter and follow-ups. Omitting changes such as all counter/follow-up's base damage decreased by 10% or them not being able to exploit.
Furthermore, anything with S.H.I.E.L.D on it will be replaced with Watchtower. Currency counterparts like Conduct Coins will be present.