The
Angel of Jubilation I mentioned in my own Hylda deck does partially shut down Koma, since it can no longer sacrifice things.
Gelid Shackles is exceptional at shutting down activated commanders, though you'll need some
snow mana sources if you want to keep Koma from swinging in.
Darksteel Mutation,
Imprisoned in the Moon,
Demotion,
Trapped in the Tower,
Stupefying Touch,
Lawmage's Binding,
Planar Disruption, and
Petrify are other good choices along this
train of thought. Removal is almost never the answer to a problem with someone else's commander, but rather finding a way to disable it and keep it there harmlessly.
Drannith Magistrate is also an option, but it will get you hated off the table pretty quick.
Board wipes in general are good for dealing with tokens, though they can be detrimental to yourself as well depending on which you choose. That
Cyclonic Rift you've got, for example, is a pretty good call if you're seeing a lot of token spam.
There's an old cycle of cards that are relevant to this as well, though not all are usable for this deck.
Echoing Calm,
Echoing Truth (Among the best budget token wipes, the only one to see reprints in Commander precons),
Echoing Decay, and
Echoing Ruin (Excellent for dealing with Treasures, Thopters, Servos, and the like, baffling that it hasn't been reprinted ever). For the record, the green part of the cycle is
Echoing Courage and instead serves as a decent budget tool for empowering token decks rather than shutting them down like the rest.
Filter Out would help if you were dealing with a large number of noncreature tokens, but in this case may not be that helpful.
Displacement Wave with X as 0 will wipe all noncopy tokens, due to having no mana value. It'll nail your own Elementals in this particular deck, but if you're in danger it's better to
reset things. Hylda can explode again quickly if you have the mana, Koma takes a little bit of time.
If general
aggression is your problem, forcing things to be tapped on entry helps too. This won't trigger Hylda as they did not tap they simply are tapped, but it still helps to buy you time and space to push your own
aggression. Things for this would be
Kismet,
Frozen Aether, or
Blind Obedience (The Extort W/B hybrid is in reminder text, not rules text, so it doesn't cause it to be illegal in a W/U deck).
This sort of matchup is also why I advise using as little one shot taps as possible and go for mass or repetition. Hylda's tokens are 4/4 against Koma's 3/3s, so aside from your Timin and
Topplegeist a
Citadel Siege will help you get triggers across multiple turns, and a
Victory Chimes can ensure you can always exploit it for another token or start pumping your board.
Speaking of her ability to pump your board,
Abzan Battle Priest and
Abzan Falconer allow you to quickly turn things in your favor as a handful of flying lifelinking 5/5s or bigger demand an immediate response.
Also, I'd like to explain exactly how good
Ensnare is. Let's say, between mana rocks, dorks, and lands, you've got 10 mana and everyone's got a pretty decent board state. You go to combat, swing all out except with the mana dorks, hold priority, tap everything for mana, and bounce two Islands to your hand to free cast
Ensnare. Tapping all your own stuff doesn't matter, since they already are, and you now have 10 mana floating to pay into Hylda giving everything you swung with +10/+10 and nobody has any blockers. This is even nicer if you have
Icewrought Sentry and/or
Rhoda, Geist Avenger out as they'll become so utterly massive they might just one shot some people all on their own.
Blustersquall, which you're already running, does an ok attempt at this too, but you'll be down 4 mana since it doesn't have a free cast option.