@TrulyAmiracle
I just finished Story mode and didn't love it.
Towers of Time are like IJ2's timed multiverses. After you finish the 4 tower tutorial, it unlocks the rest for you.
There are a few timed islands. Each island has like 3-4 towers. Just like IJ2 where each multiverse had 3-4 towers and objectives. Towers have modifiers like Ij2, like acid rain, or blood missiles or whatever. Acid rain damages you and takes away your offensive and defensive meter. Blood missiles sap your HP and give to your opponents. However, unlike IJ2, these only affect your character, not the AI opponent. You have to just git gud and overcome, or use Konsumables. These game is heavy on pushing consumables on you.
Some of the hardest IJ2 towers were trivial because you could equip epic gear on like Batman or something and just spam the same moves with dummy damage. You can't seem to do that here. So far I've found towers to be much harder than IJ2. Also, each tower has its own rewards like Koins, or hearts or jade currency whatever it is. But each island also has rewards for completing objectives. For example an Island could have 4 towers, and have 4 objectives - one for clearing each tower. Once you finish those objectives, you get the rewards, which could be skins, gear augments, additional koins, or profile icons etc.
Besides the timed islands, there are two other islands. One is summon tower where you can use tower keys to raise a specific tower with rare gear. So far I've discovered 0 tower keys. This could be like Borderlands 2's shift codes or something I dunno. Where a particularly rare piece of gear is hidden in a particular tower and you have to either use a code from NRS or find a key in the krypt to summon and clear that tower.
There are also character towers that you can summon for 25,000 koins. I haven't tried it but say you play Noob and want Noob gear that comes from Towers of Time. Rather than wait for a timed island with Noob gear as a reward, I'm guessing you can summon a Noob tower for 25,000 koins that has Noob gear as a reward. Whether its totally random rewards, or rewards of a particular rarity I don't know.
Regarding
outfits that are unlocked via AI battle.
Like Injustice 2, you can make 3 AI defender characters, and fight AI battles with AI fighters of other players. Every day, you get rewards for up to 5 AI defense wins and 5 AI offence wins. If you remember, IJ2 gave you motherboxes for AI battles. Here, I'm guessing you get AI battle reward specific gear everyday, for a limit of 10 per day.