Arbitrary form-switching mechanics - When you think about including a form-switch mechanic, ask yourself... is there a good reason why this hero needs to have two forms? What does it actually add to their playstyle? Does this solve some otherwise insurmountable gameplay problem? Why is this not just two distinct heroes? If you can't think of a good answer to these, then just make one hero. There are plenty of ways to make a form-switching mechanic, but a trap lots of people fall into is to just make their hero 'cooler' or 'more creative' by just adding MORE for MOREs sake.


Overly minion-focused basic abilities - While there is room for abilities to have minion-based impact (Raynor, Xul, Azmodan, etc.), generally speaking a hero's impactfulness shouldn't be overly dictated by whether or not there are minions nearby. As a rule, baseline abilities shouldn't be rendered useless just because there are no nearby minions. Talents are fine, and minions improving the effect is fine, but otherwise this should be avoided.


Rulebreaking for rulebreaking's sake - HotS is cool because sometimes you can make a hero who breaks fundamental rules of the game (Deathwing, Cho'gall, Murky). But sometimes people break the rules of HotS seemingly just to show how clever they are, and as a result, you end up with a hero who breaks 5 different rules, all just as incidental parts of their kit, but not really for any meaningful reason. When you break the rules, try to just pick ONE rule, then get the most out of that broken rule. Don't be a hero who has 5 heroics, 10 talent tiers, levels up independently of their team, has their own unique status effect, and treats walkable terrain as impassable and vice-versa. Do ONE thing, and do it right.


Heading-based aiming - This one's pretty simple. Don't have an ability that has you do something based on what way you're facing unless you have a good reason. The ultimate effect of performing a move like this rather than just being aimed traditionally amounts to little more than having worse controls and being more vulnerable to roots. If your hero has abilities that temporarily force them to face a certain way (maybe they have a built in "this character doesn't turn immediately" mechanic) THEN these can work, but in a game where every character can turn 180 degrees at instant speed, this is nothing but an inconvenience, and the 2-3 instances where HotS actually uses this mechanic all have justifications.


Mana destruction - Simply put, there's a reason this isn't in the game despite being such an obvious idea. Lowering someone's mana is simply anti-fun.


Bribing Already Captured Mercs - This comes up from time to time, but sorry, this mechanic can't be anything but a big "**** you" to the enemy team. Having skirmishes over a merc camp is a lot of fun, and there's a lot of nuance and fun playmaking opportunities afforded. You sacrifice all that fun and intensity when, instead of having to come in at just the right moment to steal a camp and pull it off successfully, you just... wait until the camp comes to you and press a button then the time the enemy spent capping goes to waste. Plus, bribing any camp capable of summoning others (or Turrets, which count as mercs) would be an insane amount of value. So this kind of mechanic is ultimately dead in the water, not because it would be unbalanced, but because it would make the game less exciting, fun, and skill-based. Maybe insta-kill instead of recruit-reversal would work, but even then it'd be very strong.


Unnecessary talent shenanigans - Talents are fun, but a lot of people seem to want their hero to be ･ﾟ☆✧special✧☆･ﾟ with their talents. While there are a handful of ways you can go about having fun with talents, try to avoid "this hero has 12 talent tiers". This is both because the game's UI isn't designed for it (in various ways beyond the obvious) and because it's usually just unnecessary. Additionally, the more talents you have, the less impactful each one will have to be, turning something fun into something fiddly.


Hero that replaces the core - We'll set aside for the moment that the game really can't handle another 'sits the game out' hero, as we're approaching critical mass, that's not the design's fault. There's a reason why the devs abandoned the idea of a hero who replaces the core, and a lot of it has to do with wanting the hero to have a real presence presence, to add some meaningful counterplay to their shenanigans. What's more, core-replacement heroes limit what other heroes can do ("hit all enemy heroes with X" abilities get flushed down the toilet, though you can work around that). It also limits the potential for new and exciting objectives and core designs. Such a hero would be very weird in Alterac or Towers of Doom.


Projectile blocking barriers - Ignoring for a moment that the HotS engine doesn't have mechanics in place for this, and thus most interactions would have to be coded in individually, the problem here is that every approach just introduces new problems, and the solutions to those problems creat new problems.

• 1) The shield acts as a unit to absorb projectiles - Doesn't work because not all heroes use projectiles, and most projectiles pierce anyway.
• 2) The shield simply deletes all projectiles that touch it - Better, but once again, not all heroes use projectiles, and not everything that resembles a projectile IS a projectile. Tassadar's Q is actually a moving AoE that you channel, Butcher's Hamstring is just an instant AoE effect, despite emanating from his position. Qhira's Q, Jaina's Cone, Li-Ming's laser, all kinds of moves suffer.
• 3) Just make everything that resembles a projectile be deleted - Now it just becomes subjective, and things will become confusing as players just have to remember on a case-by-case basis what does or doesn't count. Azmo's globe? Mei's Ice Wall?

On top of these, letting projectiles be deleted creates limits on what future abilities can do, and when characters have their 'high impact, long cooldown' moves deleted, it just becomes a buzz-kill.


Overly long DOTs - Damage Over Time effects that go on for an exceptionally long time are inherently problematic. Right now, the longest duration of any single DOT in the game is Xul's level 20 upgrade of his Poison Nova, which lasts for 15 seconds, but it's an effect gated behind both a heroic and a 20, isolating its problems to a very specific lategame situation. The biggest problems are that some characters lose access to major parts of their kit, or even their whole identity as a character when taking damage over time. Muradin, Olaf, and Fenix can't top-up while out of battle, stealthies can't stealth, and various other issues arise when a basic ability can apply a 10+ second dot from one hit. How long is too long depends on a lot of factors, but generally try to avoid going higher than 4. Maybe 8 if it's something where the duration stacks higher with each hit.