Of all Marvel Superman analogs, Sentry (Robert Reynolds) is perhaps the most memorable. It's not his similarity to the DC superhero which makes him a compelling godly being, but the fact that he's Marvel's own twisted version of the Kryptonian. While it is true that Sentry's powers are nigh limitless, it comes with a devastating cost; he's one of the most unstable metahumans in the Marvel universe.
There are many reasons why the Avengers are often reluctant on including Sentry on the team. All that is due to his dual nature or evil alter ego, The Void-- a dark aspect of Sentry's own powers. In a sense, he's his own greatest enemy and that's not really someone you'd want to be around with. Still, Sentry is without a doubt, among the top of Marvel's superhero food chain. He has no shortage of powers; they also seem to increase in numbers as the years go by and as Sentry also grows as a superhero. All of them are useful, to be honest, but some are better than others.
Ever seen Sentry? Dude's jacked as he should be. After all, he's the result of an experimental scientific formula which would have Captain America's scientist-makers drooling. Anyway, as the result of the experiment, Robert Reynolds' muscles turned into what every bodybuilder and weightlifter wanted: he no longer experiences fatigue.
Meanwhile, his agility also took a huge exponential leap. Reynolds' coordination, balance, and movement surpass those of the finest human athletes on Earth more than tenfold. You don't need to read that he has superhuman stamina and agility to know it; the mere sight of his physique should be convincing enough.
Sentry's superhuman reflexes and enhanced sense organs should be enough for even Spider-Man to envy him. His reflexes or reaction speed exceeds that of the speed of sound in terms of nanoseconds (or smaller). As proof, Sentry was able to catch a sniper bullet fired from a Skrull gun which is presumably more powerful and has a higher muzzle velocity than modern Earth guns. He's even shown to react faster than Thor.
As for Sentry's sensory organs, both his eyes and ears are way beyond what humans or even Marvel aliens have. He can change his hearing to any frequency and be able to hear a butterfly's heartbeat from another continent away. Moreover, Sentry can detect a single person from hundreds of miles away or in the air, even if they're above the cloud level.
Of course, superhuman reflexes and senses are useless if you cannot follow through with an equally fast movement. Good thing Sentry also has that. The yellow-costumed Superhero can exceed supersonic speeds and even chase and catch bullets mid-flight. This movement also translates into flight where he can perform interstellar travel to the sun by flying there in just mere moments.
By comparison, light from the sun takes around eight minutes to reach the Earth. That means Sentry might as well be faster than the speed of light. As such, Sentry can presumably travel distances of light-years like they were just quick trips or jogs for him. Even Thor sometimes gets disoriented with how fast Sentry can go.
How people describe Sentry's capabilities is quite hardcore. He's believed to hold the power of a million exploding suns. In Marvel superhero terms, that's pretty vivid and vast. Hence, Sentry is too damn powerful-- so powerful, that it is even theorized that he can channel the power of the sun or any light source and use it as a weapon, basically energy projection.
It's pretty standard for superheroes who can manipulate energy. What makes Sentry's different is the intensity of his energy blasts. They have been shown capable of burning the Hulk's skin, even leveling city blocks. Apart from that, he can manipulate the light around him to blind enemies, giving him a Super Saiyan glow and aura.
This one will be the last of Sentry's recognizable or relatable powers. Beyond this point, his writers went crazy with him and made him even more omnipotent. Anyway, completing the top-tier Avenger checklist is Sentry's superhuman strength. The upper limits of Sentry's strength are still unknown and still improving (goodness knows what Marvel plans with him).
As a result, Sentry can go toe to toe with a Worldbreaker Hulk (arguably the strongest Hulk version). Oh, and he can also fight Thor, She-Hulk, and Captain Marvel all at the same time with ease, even knocking them aside embarrassingly in the process. At times, even Sentry was able to beat the Void, his dark split persona through sheer strength alone. If that's not enough, Sentry can just sunbathe and absorb more of the sun's radiation to increase his strength... sound familiar?
5 MOLECULAR MANIPULATION
Superhuman strength, speed, reflexes, stamina, and even energy projection-- those are just the tip of the iceberg. Sentry is far more tremendous than that. During one of his skirmishes with Molecule Man, he got turned into a liquid, making him functionally indisposed in the fight. To Molecule Man's surprise, Sentry was able to recover from this.
Hence, it has been surmised that Sentry has molecular manipulation abilities, similar to Molecule Man. Due to this, he was able to defeat the said supervillain (who ranks as one of the most powerful beings in every Marvel universe). It should be noted, however, that he's not as proficient as Molecule Man when it comes to the said ability. In fact, Sentry doesn't even know how he did it or how to control it. Most likely, his molecular manipulation was something Void brushed up on him during their many fights and encounters.
4 POWER SHARING
What good are superpowers if you can't protect the ones you love? In this front, Sentry has it covered (your move, Superman) because he can lend some of his standard superpowers to other humans or beings. It's similar to how DC's Shazam does it and works just as effectively, meaning anyone is lucky to be friends with Robert Reynolds or Sentry.
The generous superhero has demonstrated this ability many times in comic books. However, one of the most notable power-sharing Sentry did is with a boy named Billy Turner; he turned him into a sidekick named Scout. Apparently, Sentry can also pass on some of his essences to creatures like the Hulk in order for the green monster to protect himself against Sentry's evil half, Void. All in all, it seems Sentry doesn't have problems creating new superheroes.
3 PSIONIC ABILITIES
Not convinced that Marvel might need to nerf Sentry? Turns out, he also has telepathy and other psionic abilities comparable to X-Men's omega-level mutants. Emma Frost herself, one of the most powerful telepaths who can match Professor X, once claimed that Sentry is the most powerful telepath she knew.
It's not hard to see why Emma would make such a claim; Sentry, at one point, was able to erase Earth's memory of him. Every single being on Earth (possibly even Professor X or Jean Grey) suddenly forgot Sentry existed just because he willed it. His psionic abilities are not just limited to telepathy either; Sentry has shown that he's capable of stopping a full-speed Mjolnir with psychokinetic means even after Thor threw it.
Sentry's biokinesis ability is somewhat connected to his molecular manipulation too. Since he can control matter to a certain extent, he can also affect biological material. As usual, Sentry already did this without even knowing how. It's actually both him and Void who can do this. Robert Reynolds at one point, has cured his therapist's daughter's coma and spinal problems. In contrast, Void gave a widow an incurable breast cancer with just a mere gesture.
If that's not playing god enough for you, Sentry has also resurrected someone from the dead. This happened when Ultron killed his wife. Sentry, upon seeing her corpse, grew emotionally distressed and was able to bring her back from the dead with just a touch. Basically, he can resurrect anyone-- he just doesn't know how to do it. Other times, Sentry uses the ability on himself as a regenerative healing factor-- something he probably doesn't need because of his...
Sentry is also immortal as a result of the experimental super-soldier serum which turned him into a superhero. That means he doesn't age and likely won't die. On top of that, he's also invulnerable, meaning he is pretty much impervious to any physical pain or conventional weaponry. In fact, both SHIELD and Tony Stark have yet to find or point out any physiological vulnerability in Sentry.
His only weakness seems to be his fragile mind which can be assaulted with psychic attacks. Even so, superheroes like Dr. Strange find that act difficult. Even Strange himself said that Sentry was way too powerful for magic and can resist psychic attacks, especially when stable. Regardless, no one on Earth knows how to kill or stop Sentry... no one but Sentry himself.
Sometimes, Sentry's psychological and mental instability will kick in and he'll feel guilt or remorse at the damage he causes. Afterward, he'll ask the good guys he's been thrashing around to incapacitate or stop him. Of course, if Sentry wills and allows it, it will happen. Thankfully he does often after episodes of instability due to the Void and his own mental state.