Before I begin, let’s just preface with the fact that I am a grammar Nazi.
There are many issues with how Duelyst cards are written that are able to be ignored only because it is an online card game. If it were a physical card game, the following issues would be very confusing to players trying to figure out how a card works. And, in my opinion, an online card game should be written just as well as a physical card game for ease of understanding.
Tokens – On a Magic card, tokens are spelled out (i.e. “Create a 2/2 white Cat creature token with Lifelink”). In Duelyst, they are not. For instance, Spinecleaver says “summon a Bloodfire Totem on that space” without explaining what a Bloodfire Totem is. The only way to find out is to play the card, and that is stupid. Other card games, like Elder Scrolls: Legends (may its good UI rest in peace), have the token description appear in the tooltip when you hover over a card, and that is how it should be in Duelyst as well (especially for cards like Reliquarian). I would also add tooltips for card references (like Koan of Horns explaining what a Gore Horn is), but that is not as critical.
Walls – I’m not sure how recent this update was, but Wall is now a keyword. That is a very good thing, as it makes it much more clear on what a wall actually is. I just wanted to bring this up as a good example to compare the issues below with, and to reveal one small paradox: If dispel instantly removes a card’s text, then shouldn’t Wall be removed by dispel, therefore making walls just like regular minions when dispelled instead of destroying them? 
Structures – Structure is a tooltip for a minion tribe. This is something I am very opposed to, as tribes should not come with their own abilities (after all, none of the other tribes besides Battle Pets do). To rectify this, Structure should be a dispellable keyword like Wall (and then cards like Circle of Desiccation will have to say “Structure minions”) or there should be a new keyword called “Immobile” that is applied to all Structures.
Eggs – There are no Eggs in Duelyst. There are Chrysalis Eggs, sure, but Eggs? No. By the current wording, Lava Lance should not be able to deal 4 damage, ever. There is also nothing that states that Eggs can’t move or attack. Since they are Minions, they should be able to do both. The solution is to make Egg a tribe, and give the Chrysalis Egg the Structure or Immobile keyword (that way, dispelled Eggs would at least be able to move and attack (if buffed)).
Obelysks – Just like Eggs, there is no such thing as an Obelysk in Duelyst. Making Obelysk a tribe and giving all Obelysks the Structure or Immobile keyword is the obvious solution.
Battle Pets – Battle Pet is another tooltip for a tribe, like Structure. I would fix it in the same way: by making it a simple keyword called “Uncontrollable” (or something a bit more flavorful) that would be put on all Battle Pets, which would become simple Minions. This would also allow Grandmaster Zendo to say “The enemy General has Uncontrollable,” and could open up opportunities to give Uncontrollable to other minions.
Ephemeral – Wind Dervishes are the only minions in the game with Ephemeral. This begs the question, why is it a keyword at all? Well, it wasn’t until recently. It used to be a tooltip without a keyword, similar to Structure. Now it is a keyword without a tooltip. 
And the worst part is that it can’t even be dispelled! So why is it on the card?! My solution to this annoyance would be keeping it as a keyword but giving it a tooltip, making it dispellable, and putting it on more cards than just the Wind Dervish.
False Advertising – Lies are not good (yes, I’m a hypocrite). Some cards, like the demonic version of the Panddo that comes from Pandatentiary, lie to you outright with missing or misleading text. The demonic Panddo has no text at all, but it should say “Disappears at the beginning of your turn.” Similarly, Pandatentiary lies when it says the Panddos “disappear at the beginning of your next turn,” because they actually disappear at the beginning of your turn, whether it is the next turn or not. Other cards just have unclear wording that can lead to confusion, like Dagona’s “devour ANY minion, anywhere.” Nowhere does it explain that you can’t even play Dagona if there are no minions on the battlefield.
Nonsensical Names – Ok, this wouldn’t break the game if it was physical, but it just really annoys me. I’m not talking about weird names that no one can pronounce like Q’Orrhlma’A, but names like Wild Taur (a taur is a bull, not a boar), Quahog (a quahog is a clam, not a freakish duck-man), Quartermaster Gauj (he is not even remotely a quartermaster… they just thought it would sound cool), Soul Grimwar (how could they not have fixed this misspelling by now?), and Oak in the Nemeton (makes absolutely no sense).
Flavor Text – Flavor text is great… when it is in italics at the bottom of a Magic card. Flavor has no place on the text of a card, which is supposed to be the place for concise rules of how the card is played. Text like “pull some things to this,” “a cub joins the pack,” “an ambush of Infiltrate minions,” “Forge a friendly minion,” and “a random buff” are ridiculously unclear, and don’t add flavor so much as make the card seem less official. Some effects, like the “AWESOME” BBS that Variax gives, would be too long to write out on the card, but they should still be explained in the tooltip when you hover over it.
Obviously I know that. That’s why I said it is a misspelling. 