College of the Colosseum

"sometimes I think our party likes the feeling of killing, that they like the gore, the guts, the screams of pain. Especially our barbarian, she probably became a adventurer just to kill monsters, to satisfy her rage. I wouldn't be too surprised  by this if it weren't for our life domain cleric, he keeps saying  'haha! vat a bloodbath!' and 'ze healing is not as revarding as ze hurting' and other stuff which creeps me out. If only there was a way to satisfy my group's need for death and gore without getting them hurt or destroying the local village."

-unknown bard 

With this class you get to be the leader of a DIY colosseum, where you and your friends can watch the showdown of the day. Now of course your party members won't volunteer, so that's why you need some. . . unwilling gladiators. Though it won't be all fun and games, because there is a "approval rating" for your gladiators (detailed later), which can lead to their death or freedom. That doesn't say you won't try to tip the scales though. . .

Arena of the Universe

Chose up to four unwilling enemies (which will be referred as gladiators in this subclass) within 40 feet of you that you can see. Spend a 1st level spell slot for each enemy, then roll a spell attack for each enemy, in which you have advantage on. If you succeed on at least one enemy, you, your party members, any friendly creatures, and any enemies within 40 feet not affected are teleported to a dimensional plane outside the one you're currently in. This plane has a invisible floor, has gravity, and a sphere in which you can see the gladiators affected by Arena of the Universe in the center. You, your party members, and the friendly creatures will spawn in one side of the sphere, while any enemies will spawn on the other side, each divided by a indestructible, solid, transparent barrier. The barrier will be removed if one of the gladiators gain their freedom or you want it to be removed, at which point you can fight each other. This feature will end if all of the gladiators die, gain their freedom, or you end this feature as a bonus action, at which point everyone will spawn in their last position before this feature was used and any monsters spawned by you will die.

While Arena of the Universe is active, a solid, indestructible, barrier will appear 40 feet from one of the gladiators. This barrier cannot be removed from anything besides a wish spell (just for the sake of this feature). Then for each turn you can use spell slot(s) to spawn in (via a one way portal) a wave of monster(s), hostile only to the gladiators and controlled by you. The level of the slot used determines the monster(s) spawned (detailed later). If you have no spell slots left or choose not to spawn a monster, the gladiators will be hostile toward each other until only one remains, afterwards gaining freedom.

The Approval Rating System: For each monster a gladiator slays in the arena, that gladiator will gain a positive approval rating, with the CR of the monster(s) determining the added rating.
If the gladiator has a approval rating of 10 or more, they will gain freedom. Though it can also benefit you, for if a gladiator dies, all the other gladiator will gain a negative rating, with each death subtracting 1. If a gladiator reaches -3 rating, you can execute them, killing them in a way determined by you (just make it glorious). The approval rating system does not affect gladiators in free for all mode. 

Monsters: the monsters you can spawn are detailed below, with their CR equaling the level of spell slot you use for it.

CR 1: Lion 
CR 2: Centaur 
CR 3: Giant-scorpion 
CR 4: Ettin 
CR 5: Giant-crocodile 
CR 6: Cyclops 
CR 7: Oni 
CR 8: Hydra 
CR 9: Young-blue-dragon (doesn't have lair actions or regional effects)

Once you use this feature, you can't use it again until you finish a short or long rest.

Let the Audience Decide

"Are you not entertained?!?!"

-Maximus

If a gladiator gets his freedom, you can roll a d20, which will output one of the results:

odd: a clone of yourself (controlled by you) spawns into the arena, and fights the affected gladiator. The rest of the gladiators have the Restrained and Incapacitated condition, while also being invulnerable until the end of the duel. If the gladiator is killed, the rest of the gladiators get -2 approval rating. 

Even: the gladiator gets freed and the rest of the gladiators get +1 to approval rating. 

House Rules

Master of Biomes: you get to change the environment inside the arena, including if it is difficult terrain. 

Monster Collector: you get to chose any monster with the CR of the used spell slot. DM has final say on if you can use it

Tipping the odds: poison dart traps can be set up in the arena, before the first round of combat in the arena, choose where you want the pressured plates to be. You get a maximum of 3 pressure plates.