Hand #4: Modern - Death's Shadow Jund
You're playing against an unknown opponent, on the play:
Keep or Mulligan?
I think this hand is appealing because it has a lot of 1-mana interaction already, but you can't risk keeping a 1-lander on the play even if you have follow-up interaction in case you brick. You can probably survive bricking once, but if you brick twice then you're probably in a lot of trouble.
The big thing with this hand is that, in Modern, it's not enough to "survive"—you need to kill your opponent or they will overpower you, even through discard (particularly Inquisition, which will not take away some combo pieces, such as Ad Nauseam, Wurmcoil Engine, or Primeval Titan). Sure, you can cast some removal spells, but if you're not advancing your own game plan then it's usually not good enough in this format. The fact that if you draw Traverse you probably need to get a land and if you draw Death's Shadow you're a long way from playing it doesn't help the hand either.
Hand #5: Standard - B/G Delirium (a Control Version, not Winding Constrictor) Vs. Mono-Blue Control
It's game 5 and you're on the draw. Your hand is:
Keep or Mulligan?
I don't think this hand is great, but I think it's probably good enough because you already have two sources of pressure. Sylvan Advocate isn't Grim Flayer, and they can take quite a few hits from it before they have to react, but having a 2-drop versus a deck full of counterspells is important so you can get on the board before they can, and you have that. If you manage to draw 2 sources of black mana, then you can actually curve 2-3-4-5, which gives you hope to resolve something before they can cast their draw spells, and I think that's pretty good.
If I were playing a B/G Constrictor deck, however, then I probably would not keep this hand, because some of your early pressure cards are black and you can't cast those (so if you draw Winding Constrictor, for example, that's quite bad for you). A control deck shouldn't have many black cards post-board to begin with since the removal is bad versus mono-blue, so you can afford to not draw Swamp for a while and still be OK.
Hand #6: Standard - B/G Energy
You're on the draw against an unknown opponent. Your hand is:
Keep or Mulligan?
I think this hand is interesting because, at first glance, it's a functional hand. You have creatures, lands, and removal spells, both your colors, and you can already cast some spells. Upon further inspection, however, this hand seems to be very clunky. You can't actually cast any of the cards in it!
For this hand to be good, you need to draw a source of green mana in your first 2 draw steps. If you draw that, then you can play a turn-2 Rampager and a turn-3 Tracker, which is good but not amazing. If you draw a turn-1 Attune with Aether then that's just the great.
If you do not draw a source of green mana in the first 2 turns, then your hand is quite bad. We're likely looking at your first play on turn 3, and the whole hand is going to work awkwardly. You have to play a turn-1 Forest to Rampager, so you won't be able to play Grasp on turn-2 even if you draw a Swamp. You'll get to a point where you will only be able to cast one spell a turn for many turns, and that's not amazing when you start on turn 3.
Overall I think the risk with this hand is too high. There's just too much tension between the cards in its hand. If you're going to play only one spell per turn, then they have to be really good spells or you have to start very early, neither of which is happening with this hand.
Bonus: Keep or Cycle?
We hit an interesting decision we disagreed on during testing, so I'm presenting it here. You're playing an under-powered B/W deck in Amonkhet Draft, and you're on the draw. You play a turn-1 Plains and your opponent played a turn-2 Forest, Plains, and Initiate's Companion.
Your hand is:
Do you cycle Winged Shepherd at the end of the turn or not?
The actual answer probably depends on the contents of your deck for you to judge on the spot, but I think it's interesting to think of the factors that would make you keep it or cycle it.
Keep it, but there are certain deck lists that would make me cycle.
When I first looked at the hand, I assumed you should cycle it. I thought you couldn't afford to do nothing in the early turns, and had to cycle to find a turn-3, -4 or -5 play. I also knew you had a Gravedigger in your deck, and cycling it early is much better if you do draw it.
After talking to my teammates, though, I realized I was just wrong, especially because the deck is somewhat under-powered, and if you cycle your 6-drop when you have 5 lands already you're probably not going to win the late game. This 6-drop isn't a good 6-drop, but it's a card that's capable of winning the game, especially against G/W, and this deck didn't have many of those. Even if you do draw a 3- or 4-drop, you're going to stall the game into nothing and you'll eventually lose. Besides, your 2-drop could just die, in which case you can spend your turns bringing it back. The fact that it's Trueheart Duelist specifically means that it can hold off attackers for quite a few turns, and your opponent probably won't attack even if they have something like a pump spell.
I think for it to be right to cycle this card in this spot, you have to have a deck with a lot of power in it—particularly late-game power—so that you can afford the chance to be strongly flooded in exchange for the chance to draw some early creatures and stabilize. If you have multiple Gravediggers or other ways to return it from the graveyard later on, then it's also a strong point in favor of cycling it. As it was, though, I think it was just a mistake to cycle in this spot.