I'm not a designer, but I am a person that sees no issue with those two features as written, so maybe I can provide some insight?
1. Shadow Step. It's not as "at will" as you've phrased it because it requires you to be in dim light or darkness, and to be able to see an unoccupied area you actually want to teleport to that is also in dim light or darkness. Bright light shuts it down, and isn't all that hard to come by, plus it takes your bonus action so you are typically losing out on extra damage from an attack, or some other noteworthy benefit, to get advantage on a single attack assuming the power is fully utilized - which is typically not going to be a significant change in how fast you take down an opponent.
Yep, I acknowledge the limit on when Shadow Step can be used. But, unless your entire campaign occurs outdoors during the day, it isn't actually that uncommon for a monk - particularly one with darkvision - to be in dim light or darkness, and where they want to go to be in dim light or darkness. While encounters in occurring completely in bright light aren't unusual, frankly, neither are ones in which there are patches of dim light or darkness. So, by "at will", I don't mean "you can use this at any time, anywhere". It is, however, an unlimited resource, that can be used frequently. There is nothing to prevent a monk using it a dozen times in a combat in which there are patches of dim light or darkness.
I have several other issues with no-cost teleports. First, they make physical challenges redundant. Chasms and pits, high ledges, water/acid/lava pools, etc. etc. are easily bypassed or ignored. Again, I have no problem with PCs using limited resources to deal with such problems - that's expected, and consistent with the D&D game design philosophy since year dot. But, again, Shadow Step is
resource free.
Second, as an extension of the first, they make minions in boss fights redundant. There's no having to "get past/through" the hordes of mooks to the evil boss if you can just teleport past them and lay the smack-down. Again, I have no problem with this
if it costs you something (and I mean, something other than a "bonus action", which is, by definition, a bonus to your ordinary action and move).
Third, for monks, using a 60-foot teleport as a bonus action means they are able to move, in any given round in which they can use Shadow Step, at least 100 feet. And still make two attacks. The 6th level wood elf monk in my campaign, with the Mobility feat, can move 120 feet. It's like he's the friggin Flash. At 6th level. I'd be prepared for this sort of shenanigans for a 16th level monk, but 6th level?
Fortunately, for me, the solution was simple. Using Shadow Step requires spending 1 ki point.
2. Stunning Strike. It isn't as good as you make it out to be, since it requires both a successful attack roll and a failed saving throw, doesn't apply as deadly of condition, and also has a specific finite duration rather than being potentially multiple rounds of lost actions from a single resource expenditure.
To put the more important trait there, the needing of both a successful attack roll and a failed save to work, into perspective; let's imagine that the monk has a 70% chance to hit the target's AC, and the target has a 70% chance to fail the save. That means there is actually a 49% chance that the target is stunned while the chance for a successful hold monster against the same target is typically going to be much higher.
And even your statement that it can be cast up to 4 times per round isn't completely accurate because it accompanies your other statement that it can be cast monk level times per short rest - you can't actually make 4 attacks in a round without spending ki, so if you do one of these things you can't do the other.
Yep, I agree I was a bit hyperbolic. However, while it isn't as "good" as perhaps I've intimated, it's still ridiculously over powered for the level at which it's gained. Combine Stunning Blow with the Shadow Step, and there's very little chance the monk missing the first attack. Combine Stunning Fist with a Flurry of Blows, and the monk gets three or four chances at stunning the bad guy (Yes, I know you can't combine Shadow Step with Flurry of Blows). Sure, the monk might have used most of his ki points if he misses a few times, or the bad guy saves a couple of times, but basically, he's almost guaranteed to stun the bad guy. Until the end of his next turn. The bad guy doesn't get to save at the end of his turn, like he does against just about every spell that would incapacitate him. So the whole party has a guaranteed full round of wailing on a bad guy that cannot possibly do anything in response. Bad guy, if he survives the round, then tries to run away, and because Stunning Fist can be used with any unarmed attack, monk has another go at stunning the bad guy using his reaction. Way to make for a fun boss fight.
The above means that the monk keeps all of his ki points in reserve until the boss fight, and then unloads on the boss. So the design of the power drives particularly disappointing play behaviour - that of the "nova" round and the 5-minute-adventuring day. Sure, no-one "forces" the player of the monk to do this, but I query the design of a power that screams "spam me".
Not only does Stunning Fist have no action cost (it's not, e.g. once per turn, but can be used with any, and all, unarmed attacks), it has very little resource cost - 1 ki point. A monk gets all of his ki points back after a short rest. Want to trying stunning bad guys 20 times a day? Sure can. Although the action economy has always been a thing in D&D, designers really started thinking hard about it - and making sure it "worked" - in 4E. And how rare and high level were stun powers in 4E? Stunning breaks action economy. It screws over the stunned target completely. That monks in 5E can stun opponents
from 4th level, repeatedly, at very little real resource or action cost, is, in my opinion, a
curious design choice.
Of course, this is all Just My Opinion(TM).
Cheers, Al'kelhar
