Most of the answers here are Outdated, so I thought i’d give this an updated answer.
The use of Potara earrings is now allowed
Kefla is the result of Fusion from Potara earrings in the Tournament of Power
Items of any kind are allowed as long as it Amuses Zeno
As of right now , Episode 125 , Fusion is becoming more and more of a Possibility.
Frieza is very very injured, almost dead to be honest by Toppo’s sudden increase in power as he unleashes the things he has been taught by belmod and becomes GoD-Like,he is still on the stage tho , which is a good opportunity for a Sneak Attack if he regains any stamina during the 6 minutes left.
Android 17 , tho having Infinite Energy is an advantage in almost every case,it is not on this one,Because Toppo has an “Hakai” energy that surrounds his Body,so every attack that comes into contact with it is Erased.
Goku & Vegeta , are fighting Jiren , Vegeta with his New Limit-Breaking Form that seems to be stronger than Kaio-ken x20(although not by much) and Goku with his Kaio-ken , Jiren still seems to be holding back and easily handling them combined.
Vegeta is fighting Toppo next episode , which leaves Goku and Jiren alone , Goku has to go Ultra Instinct if he wants to stand any kind of chance against Jiren Alone, and Vegeta by my estimation should be able to overpower Toppo , seeing how he overpowered Jiren in more than one occasion.
So the only way Universe 7 can assure their victory is Potara Fusion or Metamoris Fusion , even tho for a short time , it will provide enough for Vegito/Gogeta to slap Jiren and possibly Toppo Too as long as he’s fused , because remember , Vegito is as strong or stronger than Goku(usually) ‘s strongest form in just his Base,meaning that Yes Vegito can beat Jiren.
It all depends on how Toriyama sees it fit,there are only 6 Episodes left before DBS Ends for this year , so the tournament of power has to end 5 Episodes from now,the only way this can happen that quickly is either Fusion , or Goku masters Ultra Instinct and combines with Vegeta for a final attack that somehow eliminates Jiren.
Spoilers for Episode 128&129.
To all of you who thought Vegito is making an appearance,i’m sorry but it isn’t happening,Vegeta has been Confirmed to be eliminated in Episode 128. But Don’t Worry,something good is coming in Episode 129.
Episode 128’s Title : With Noble Pride to the End! Vegeta Falls!
Episode 129’s Title : Transcending The Limit! Mastering Ultra Instinct!
So yeah,Goku apparently Masters Ultra Instinct during this Arc,something Beerus hasn’t been able to do for Millions of years,Talk about talent…
These Spoilers are true,they’re from a very reliable Source,so sadly Vegito is not making an appearance in Dragon Ball Super , unless it comes back next year with new arcs,we won’t be seeing Vegito any time soon.