Warning: SPOILERS for Avengers #65
Two of Marvel's most dangerous villains have destroyed the universe in the exact same way - and yet Mr. Sinister and Loki still manage to lose. Supervillains are found often in the Marvel Universe, but Sinister and Loki are of a kind; both appreciate mayhem and chaos and attempt to spread it as far and wide as possible. But in Avengers #65, the Loki variant Avenger Prime proves he's just ad deadly as Sinister - and has just as much luck.
Mr. Sinister and Loki may appear to be haphazardly constructing plans as they cause chaos on a whim, but they are both fiendishly smart and are not to be underestimated. Nathanial Essex's genius-level intellect and breakthroughs in cloning have allowed for the X-Men to cheat death; the Krakoa era means no mutant can truly die, thanks to the Five mutants and Sinister's genetics laboratory. For his part, Loki has plans within plans, and while he does not seek to destroy Asgard and the world, he always attempts to rule it - but the Avengers prevent this from happening again and again.
In Avengers #65, written by Jason Aaron & Javier Garron with art by David Curiel, the Loki who would later become Avenger Prime steadily grew his power over the years, eventually defeating the Avengers and preventing their ascendance in his universe. All other superheroes and even the entire nation of Wakanda fell to him - and when supervillains that the Avengers would have stopped began to arrive, he took care of them as well. Unfortunately, the takeover had a price: the life of every being in Loki's universe.
Loki and Mr. Sinister Take Over The World - And Still Lose
These events eerily mirror those in Sins of Sinister #1, in which Mr. Sinister carries out his masterstroke plan: by manipulating the genes of every mutant newly resurrected, Mr. Sinister's clones can effectively control every member of the X-Men - and by extension, mutantkind. Soon, Sinister is able to take over multiple governments and wipe out any superheroes who stand in his way - the Fantastic Four, the Avengers, even magical characters like the Scarlet Witch. Even so, Sinister has lost: the clones have free will, and someone has broken into Mr. Sinister's laboratory and stolen his Moira clones, meaning he cannot send information to the past or receive it from the future.
This means that Loki and Mr. Sinister have both obtained everything they ever wanted, but the victory leaves both men hollow. Sinister has far less control over his subjects than he initially desired, and Loki has no subjects to rule, not even other Gods (since they all perished). Loki and Mr. Sinister are more alike than they appear - and the villains of the X-Men and Avengers respectively manage to snatch defeat from the jaws of victory every time.