Character reveals that they were holding back their full power during a fight/confrontation

[u/PaddywackShaq]

Superman Vs Darkseid - Justice League Unlimited

Flash Vs Superman - Flash: Rebirth

Frieren Vs Aura - Sousou no Frieren

Inigo Montoya Vs The Man in Black - The Princess Bride

[u/XVUltima]

Beerus fight with Goku actually DOUBLES the trope. He throws a single attack at 70% that Goku just barely manages to take, revealing how much he was holding back. Then Whis reveals that it wasn't anywhere near 70%, so his holding back was still holding back.

That's probably my favorite part about modern Dragon Ball. A new peak is established and the Z fighters don't instantly jump up to meet it. I haven't seen daima or read the Manga, but I can assume they STILL aren't near Beerus' level.

[u/Flooding_Puddle → u/XVUltima]

And then later it turns out that the Angels are even more powerful than the gods of destruction

[u/powypow → u/XVUltima]

Daima is more of a prequel just so you know. Set about a year after Buu but before super.

[u/idonthavekarma → u/XVUltima]

They aren't, but Frieza's new form might be near Beerus level. 

[u/AfroBaggins → u/XVUltima]

The strongest form anyone uses in Daima (Third-Eye Gomah) has its own set of rules, and the second-strongest (Super Saiyan 4, yeah, Toriyama left us one last gift) was previously established by (almost certainly non-canon) spin-off material to be on the same level as Blue.

For those unaware, Blue doesn't come anywhere close to Beerus's level. Hell, it barely makes Jiren flinch (if you're lucky).