Artificial Human: The Innocent are artificial people made to make up for the population destroyed by the Great Destruction. It seems they end up almost all the menial jobs, leaving all the normal people to either be Demon Busters, Shopkeepers, or Guardsmen.
Congrats, you just made a character who can dodge, block, and counter at any moment. Good luck winning any battles with more than one enemy. Also your use in battle is very low, only being slightly better than "The Load" because you have a small chance of dying. However, this is a good focus of non-combat characters, as it allows you to level by going into a party, but not a good focus for a fighter.
The Dimensional Incision skill. It's a gunner skill with an almighty affinity, something a lot of people have wished for the Magic Bullet chain expertise to have. However, it costs a horrid 50 MP (all other gunner skills cost 5 MP at most), and since the only enemies weak to almighty are Slime, Blob and Black Ooze, it's better to just use something else.
Same thing with the Dimensional Laceration skill, which is pretty much the same as the example above, but it's a melee skill, and costs 50% of your max HP to use.
Become a Real Boy: Some of the Innocents have gained sapience and built their own community in the hollows of one of the destroyed communes. This has since become the Neutral factions' home base.
Disk One Nuke: Having a character master counter/dodge/block, at least two usable skills of each, means you can solo any enemy, however that isn't the same for groups of enemies, as counter takes some time to prepare. Despite that, you can distract a boss, and possibly kill, at any level as long as they don't use any special statuses.
Everything's Better with Spinning: The Spin expertise. With the implementation of channel unification, the game now disconnects players who stay still for too long. Players then found a way for their characters to stay spinning in place constantly to prevent this.
Human Resources: Plasma, lovely floating spheres of light, which Demon Busters can "communicate" with to scavenge materials are made out of the souls of people who died in the apocalyptic flood.
Improbable Weapon User: Improbable armor is even more common. Wearing a full Kimono and a blade made of glass to fight Yamato-No-Orochi, is just one of the epic things you can get done in this game.
In-Universe Game Clock: Each hour in-game takes 2 minutes in real time. Also, each 12 hours in-game represent one phase of the moon. Some stores only sell specific items during a specific moonphase, and some enemies only spawn during a specific hour or moonphase.
Law Enforcement, Inc.: The Demon Busters come off as this (with elements of Heroes R Us), considering how many of their missions involve providing services/protection/vengeance in exchange for goods or money.
Level Grinding: It takes more experience to get from Level 96 to Level 97 than it does to get from Level 1 to Level 96. Mathematically, the amount of XP needed to get from 96 to 97 is TWICE the amount required from 1 to 96, and more than FOUR TIMES the amount required to go from 1 to 95.
Level Up Fill Up: Players also get increased movement speed and damage for 5 minutes.
Loading Screen: Originally, the game didn't have them, but after the channel unification, specific areas require one. While in the japanese server it usually has some advertising of new items or new content, the US server has drawings made by players. Aeria Games used to have one event to make new ones every 6 months, but apparently Atlus Online isn't going to follow this.
Magikarp Power: The Rapid expertise. You start with a weak skill that shoots 3 times, then you get a skill that always deals 49 damage total (and for that reason it's used to grind the expertise), then you get a skill that shoots 4 times, but has so random a damage that one of the hits usually hits below 10 damage. Then you get 13 Shots to Hell, which shoots 14 times, each of which is more powerful in raw power than most non-spell attacks in the game.
Obvious Beta: Most new contents are obviously not even tested. Special mention to version 1.605, which fixed one minor bug while introducing a crapton of others, some of which were pretty awful. In this particular case, it was impossible to revert the update, because it changed the entire game's build (the "update" actually had you download the whole game again).
Back in the first implementation of the Denshi Kairo dungeon, so many things were bugged that they had to take the server down the next day to revert the update.
Aeria Games's Game Masters (and even some Game Sages) would always claim that they tested content extensively before implementing. One would think "extensive testing" would make them notice that the most popular dungeon (Old Ichigaya Camp Gold) is lacking AI, or that the most rewarding cash run bosses (Shiva & Vishnu, which were being spammed to hell and back at the time) are lacking two thirds of their HP, or that the soulstones they just implemented are not working at all.
Atlus Online isn't much better. They apparently have no testers at all, and have to have the players test their contents. This was made rather obvious when they tried to fix the PvP bug twice, but players confirmed they failed half an hour after the maintenances. They also needed player confirmation when the bug was actually fixed on the third try.
Repeatable Quest: There is a small variety of these, including quests you can only repeat if you pick up uncommon loot.
Relationship Values: Contracted demons can range from "Wishes Death on-" to "Linked by Fate with-" towards the player controlling it. Demons receive attribute bonuses with high friendship and penalties with low friendship. High friendship demons also give you daily quests.
Run Don't Walk: Players cannot walk at all. They do have a walking animation, but you can only see it by moving towards a wall and holding the move forward command.
While generally averted due to this being SMT, it's played hilariously straight with the Traesto spell; every character has it to start with, and it is, as always, your "return to saved spot" spell. But it takes so long to cast that you could probably just walk and get where you're going faster. Traesto Stones, the spell in item form, are instant.
Estoma: It makes enemies lose their aggressiveness towards you for a small time frame. However, its range is so short that it's unusable.