Alright, so I just scrolled through the list of all Pokemon abilities. I came up with some that I have no reservations about and some that I do. Personally, I believe that it's going to be very hard to overshadow Magic Guard, so we should focus our efforts on not overshadowing Trace. To achieve this, I was inclined to look at some doubles only abilities.
First up, we have Minus and Plus. Being an electric-type Pokémon, Krilo would fit right in with the Manectric line for Minus and the Ampharos line and Dedenne with Plus. It doesn't particularly matter which one, as they're both useless in single battles, since the opposite ability is needed to make the ability function. If you're looking for an electric-themed, singles-useless ability, these two cut it pretty well. A similar ability in this category that I'll make note of here, though I don't particularly care for it, is Battery. It serves a similar function to Plus and Minus, being electrically themed and only working in Doubles, however it is a signature ability and the only Pokémon that currently has it has a design specified to fit that ability, hence why I don't support it for Krilo. I merely mention it for the sake of thoroughness.
Moving on to abilities with no technical use or no important use in singles, I believe Damp and Illuminate may fit the bill. Damp only affects Explosion and Self-Destruct; moves which are objectively seen used very little in the meta. Seeing as Krilo is a shrimp, and shrimp live in the water, which is wet, Damp thematically makes sense. The Pokémon in game that get it, excluding the Paras line, all are different types of aquatic and semi-aquatic life. Hence, there is no reason a shrimp could not get it. Illuminate is a bit more random, but personally I just see the bright yellow lines on its body, and they look to me like they would glow in the dark. That's probably just me, but I'll throw it in the mix anyways.
Lastly, I come to abilities I can see as working thematically, but might overshadow Trace. Trace is already marginalized by Magic Guard, so we really shouldn't be trying to even come close to overshadowing. regardless, I put these forth as hesitant suggestions, merely acknowledging them as flavorful in some manner. First up is Hyper Cutter. The potential benefit to this is that it increases very slightly the ability of Krilo's physical set through making it immune to the Attack drop from some moves and Intimidate. Again, it's super niche, especially since Krilo's physical set is currently pretty terrible; however, if we end up slightly expanding that set's capabilities, the ability may become a bit more useful. As for the flavor aspect, Krilo (I believe) is based off of a pistol shrimp, which are known for having one large, more powerful claw that can create an instant of cavitation that comes close to 4,700 degrees Celsius, rivalling the surface of the sun (5,500 C). I could explain more, but it's mostly just about that claw. Keeping this moving, next is Shell Armor. As anyone who has ever cooked with non-deveined, non-peeled shrimp can tell you, shrimp have a shell. They're not terribly sturdy or anything, but they exist. The ability itself pays homage to that shell. The potential benefit is that the already semi-bulky Krilo now gains an immunity to critical hits. Krilo doesn't currently have a form of recovery outside of items, so it's not a terribly big deal, but it's still something worth consideration. Lastly, I come to Hydration. A variety of aquatic Pokémon get this ability, so I extend that notion out to shrimp as well with my mention of it here. Really the only flavor for this is that it's associated with water types, and shrimp should generally be kept hydrated to let them live... There's also that weird thing from like, the 70s, with the brine shrimp that you could put in water (That's what Sea Monkeys were in case you didn't know). The competitive possible use for this is the ability for Krilo to run Rain Dance (possibly Z Rain Dance), Rest, and then two attacks to basically just keep staying alive until it runs out of PP. Out of the three abilities I'm reluctant with, I'm most so with this one, due to the potential to just overcome anything that can't outdamage Krilo, but it is slightly flavorful and requires a specific, possibly underwhelming set. I don't know, I haven't experimented with it. I believe it is the most likely to outclass Trace out of my suggestions, so I urge extreme caution if you may want to consider this one.
Anyways, that's all I really found, so I'm going so respond to some of the ideas posted in the time it took me to write all of this. Hmm... I'm glad I wasn't the only one who thought Illuminate was a thing... Battery, again, signature ability and Charjabug is designed to look like a 9-V battery so... I'm quite hesitant on that. Static I think is interesting... It fits the electric typing very well, but I'm pretty sure the ability to passively punish many physical attackers with status would directly compete with Trace, which is basically a luck of the draw ability that depends on what your opponent happens to bring. Wonder Skin I personally think falls into a similar box as Static. It can fit, yes, and I myself even briefly considered it, however the ability applies to ALL non-damage moves. That means if we give Krilo a bit more expanded status movepool, Taunt might suddenly become useful, and then Wonder Skin has more use than Trace. I don't think it's a bad suggestion, I simply want to point out that there may come a point in the future where that ability overshadows Trace, which we're trying to avoid. Telepathy is interesting, and definitely not overshadowing. It plays on the mysical aspects which jas pointed out in his post. My only thing is that Telepathy appears to only be on Psychic types or legendaries. The only exception is the Noibat line, and I'll be honest, I have no clue why they get it... Maybe it's something with echolocation or folklore, I honestly don't know. Schooling is a form change ability, so while it does not technically activate on Krilo, I'm sure the program would bug out or something weird like that. Besides, according to the internet, the most reliable of sources, shrimp actually don't school. If they do, it's usually during spawning season. If we're talking about krill, then it's called a swarm of krill just as much as a school I guess. You learn something new every day I guess. Anyways, I think that was everything, though I might have missed something.
If you're wondering my personal preference, I quite like Hyper Cutter if it isn't too useful. After that I like Plus/Minus, Illuminate, and Damp.