Goku and Vegeta are incredibly powerful beings, as such, it can be something of a challenge to come up with threats that would give them a run for their money. Now, according to "Death Battle', the two are still weaker than Superman, which would appear to help. However, it's also been made explicitly clear that these two were the strongest beings in the universe and that was before they acquired literal god modes.
"Super" has made an effort to show that even Goku and Vegeta can still be severely outclassed, but it still seems like we're getting close to hitting a potential ceiling. I mean, there are only so many ancient beings that can be reawakened and the more mortals you introduce to challenge them, the less impressive their powers seem. Still, the story must go on, so what do you do? Some ideas have popped up and I figured, why not lay them out?
1. Replicators
For those who haven't watched Stargate SG-1, the Replicators were these creepy robot spiders that consumed matter (organic or inorganic) and used that to multiply (or replicate, if you will.) They were a force to be reckoned with in the show, repeatedly overpowering the show's normal big bads, the Go'auld, and posing a threat to the galaxy as a whole.
Now, you could point out that the robots were taken out by regular gun fire, so the Z-fighters should be able to easily take these things out, right? Not necessarily. While the robots themselves aren't all that formidable, there are a large number of them and the number only gets bigger. As such, it wouldn't be that much of a stretch to see Goku and Vegeta get either overwhelmed or just worn out trying to take the robot horde down.
In fact, this particular enemy gives the other characters a prime chance to shine without it feeling forced or clunky. This isn't one super powerful being, but a massive amount of weaker ones that make up for said weakness with an unending swarm. If that isn't enough to make the case,remember that the animated version of the Justice League took on a similar opponent in an episode and even the full might of their then 50+ hero roster was barely able to keep them at bay. Thus, saying that they could give the Z-Fighters a good go isn't too much of a stretch.
Even fitting them into the established universe isn't that difficult as it's just tech (nano-tech specifically). All you need is a scientist (Bulma, an aspiring rival, or an alien one) who creates these things, perhaps even with good intent, and it just goes awry.
2. Zombies
Like the Replicators, zombies are a threat that thrive on numbers. The individual zombies aren't so daunting, but the massive numbers would be the factor that makes them a threat. Some tweaking regarding the rules of infection would be needed so that characters can get bitten, but not immediately turned, but other than that, I could see this working out well.
While they don't have regenerative abilities like Cell or Buu, the take out the head rule means that the Z-fighters can't just blast off limbs or blow holes in torsos. They'd either need to aim rather well or make large enough blasts that the brain gets taken out with everything else. One interesting twist here is that Krillin's Destructo Disc would be a useful and even formidable technique. Speaking of, like the Replicators, the zombies are a threat that could incorporate the other Z-fighters in a believable fashion.
You might be thinking that they can fly, thus just rain down ki blasts with impunity; but remember that collateral damage is still a concern and they have to land some time. On top of that, this approach doesn't guarantee results. They could ki spam an area and only take out a few zombies if the blasts don't land right. Fatigue would very much be a factor that could make this a tougher fight than you might think.
Incorporating them into the universe wouldn't be too difficult either. You can go with a virus or some sort of mystical incantation that brings the dead back wrong. It's simple and still fits within the established rules of this universe.
3. New Life
The main job of the Supreme Kai is to create life to populate the universe. Unfortunately, the Tournament of Power arc showed that universe 7 is sorely under-populated. As such, it wouldn't be too much of a leap to have him make an effort to rectify this short coming. Still being something of a novice, some of these could end up posing a problem. Maybe he tries to create beings that can compete with the saiyans and the forced rushing of the process is what does it, or maybe it's just law of averages and there are some "bad eggs" that go along with the more benevolent beings that he creates in his endeavors. Either way, it would give the writers room to work with going forward.
This doesn't just aid the villainous end of the scale, more new beings means more potential allies who could offer assistance from time to time. It could widen the scope in many respects and create a more expansive universe both literally and figuratively.
4. Multi-versal threat
With the multiverse established, it makes sense to threaten it all. This would likely be another ancient being that's been imprisoned for eons, but rather than just pose a threat to Earth or universe 7, it would threaten all of them Not only would this bring in the other Z-fighters, but the characters from other universes to all stand together to take this thing down. Unlike the last multi-versal threat (the ToP), this would have the fighters fighting alongside each other as opposed to facing off.
Whether it results in a universal consolidation like DC's "Crisis on Infinite Earths" or not, it would still be a huge story with massive scope. Seeing the Z-fighters, Pride Troopers, the Trio de Dangers, the universe 6 fighters , and the rest all banding together would be a hell of a sight, if I do say so myself.
Any thoughts? Suggestions about what else the heroes could face gong forward? I'm interested to hear your thoughts on the matter.
