I had to whittle the list down a lot. That's why her feat section is so small, but roughtly the same length as the outliers.
Also, I'm planning to revise some Frieza to Cell scaling DBZ.
No Training
There's actually evidence that Android 18 is significantly stronger than her Android Saga self: during the Tournament of Power, 18 blitzed Shin faster than he could react and terrified him.

Android 18 wants to Kill Supreme Kai
If you don't understand why this would make her way more powerful, then I'll break it down; according to
Daizenshuu 7, the Cell Juniors are equal in power to Vegeta and Trunks at the time, which
Cell seems to confirm.
- Children which perfect-form Cell births through his tail. In the story, he gives birth to seven. Their appearance is like perfect-form Cell, only small and cute. However, their power was equal to Vegeta and Trunks at the time, and their personalities were cruelty itself.
This takes place after
Vegeta and Trunks went into the Time Chamber (it's heavily implied he went into the Time Chamber, as his hair goes from short to shoulder length in a few days). While Vegeta doesn't use Grade 2 during the fight, Trunks (
who was nearly equal to the Vegeta that stomped S-PC before training agai)
does briefly, though he later goes Super Saiyan
throughout the rest of the battle.
Piccolo was shown to be the only one standing alonside Trunks and Vegeta, and he's way more powerful than before he went into the Time Chamber, even while using his weights. Piccolo, as you know, was comparable to 17 and
superior to 18. Buu Saga Piccolo (seemingly having trained in the 7 year gap) is at least comparable to his Post-Hyperbolic Time Chamber self during the Cell Saga, and
Shin is way more powerful.
Basically, Android 18 (Android Saga) < Android 17 = Piccolo (Kami) <<< Imperfect Cell (Humans Absorbed) << Semi-Perfect Cell < Piccolo (Post-Time Chamber/Buu Saga) < Cell Jr < Shin < Android 18 (Tournament).
Plot Introduced Stupidity/Outlier
PIS

Krillin And 18 VS Shosa
Logically, it actually makes more sense for this fight to be Plot Introduced Stupidity; Krillin and 18 are husband and wife, so the creator of this episode wanted a sort of touching moment between the two of them (god, this is awful to write), such as fighting together against a common enemy.
It also gives Krillin a window of opportunity to be eliminated. The same goes for the fight with Majora, which happens in the same episode.
There's also the fight between
18 and Ribrianne. You'll notice that 17 is also fighting Rozie here and struggling, so it's most likely bad powerscaling, especially since this turns into another husband and wife moment for Krillin and 18 right after.
Outlier
There's a limit to how far this excuse will go. Generally her feats of grossly overpowering
Large Star level and
Universe level characters grossly outweigh any scaling to Krillin. Here's a small list
It's also worth noting that she
kicked away an attack that Krillin couldn't and that Cocotte is powerscaled from 18, not the other way round.
She has just as much evidence for
Universe level as
Large Star level, so what about
Large Star level, possibly
Universe level? Cocotte is exactly the same as well, as are most of the higher Pride Troopers.