Zahndrekh's Bag of Tricks Part 2: The Right Tool for the Right Time

Decided to split this up into two because the other section got so long. Zahndrekh really is that good.

The big thing that people are fascinated by is his ability to choose a Warlord trait. Good set Warlord Traits are good to come by. Being able to choose from the army's list is even better. Better than that? Being able to choose from the BRB lists. Oh yes. Even though you can't use the same one twice, and Turn 1 you're using Zealot, but from Turn 2 onwards you have choices. Make use of them. You're not going to use every one every single game, and some you may never use in your entire life, but know what you have.

Red indicates something actually useless for one reason or another. Blue ones are going to be ones you'll use very often. Everything else has a use, sometimes rather situational though.

Necron:

1. Eternal Warrior. Good when it comes up. Zahndrekh wants to be as far away from Assault as possible, and he should have a retinue to keep those pesky ID guns away from him, but occasionally he'll need it. And you'll want it when you need it, a one shot Warlord sucks. 
2. Zealot. Not terrible, though if you want to keep it you'll need to hold onto it and not switch, which can be limiting. If he's part of a Lychstar or hanging with Flayed Ones for some reason, it's a good option.
3. Reroll Fear/Pinning/Morale bubble. Pretty good again, but LD 10 means you should be passing these more often than not. Though, if he's not in combat but a unit in the bubble is, he can give this to them so they don't run.
4. Reserve Manipulation. Obviously good... if you have reserves. Scythe are still pretty good, so you will probably have them.
5. 12" Relentless and Crusader bubble. Suddenly you can Rapid Fire and Charge. Not bad by any means, but again, very situational.
6. Must always issue/accept challenges, gets rerolls in a challenge or Hatred. Hahaha no. If you need help in Assault, there's other options. I can't think of a time where I'd want this over Fearless/IWND, reroll 1s in Assault, or even Furious Charge or Counter Attack.

Tactical (skip if playing Eternal War):

1. Discard 2 Cards per turn instead of 1. Not bad if you want to, you know, discard 2 of your Cards. VPs win games, and sometimes getting a better hand is better than getting a buff or USR.
2. Force your opponent to discard a card. Awesome! But, if you think about it, it's pretty happenstance. You need to know that they have a card that they will for sure achieve the next turn and will give them an advantage, and then they might draw a good card anyway. If you know for sure they have a d3 (or 2 VP in Tournaments) card that they're likely to achieve next turn, it might be worthwhile.
3. Generate an extra card on your first turn. Can't use this.
4. Can discard and redraw all cards on your first turn. Can't use this.
5. Reroll dice for d3 victory point cards. Not bad, but many (if not most) tournaments have been ruling all d3 victory point cards as 2 VP. And these are very rare and hard to achieve anyway, usually getting discarded or scored as the 1VP version. So... meh.
6. Gain an extra VP if the warlord scores a "Secure Objective X" card. This is pretty good, probably the easiest one to take advantage of on this table.

Command:

1. 12" bubble of use Warlord leadership. *Looks at Necron book.* *Everything LD10* *Pass*
2. Enemies within 12" use lowest leadership instead of highest. I mean, super situational. If it's very important that the opponent fail the Morale test and it's a very big difference between the highest and lowest LD, maybe consider it. But picking this over other options is pretty iffy.
3. 12" Move Through Cover bubble. I mean, it's good, but if you think it's really that important you can just be a Decurion or take Zahndrekh as part of a Royal Court. If you want a straight CAD, it might come up more.
4. Add 1" to Run or Charge in a bubble. Nice, if you're running something Assault oriented such as Lychstar. Not so much for shooty Crons though, but nice if you want to assure getting to an objective.
5. 12" bubble reroll 1s to hit in shooting. This will probably be your biggest go-to trait.
6. 12" bubble of reroll 1s to hit in assault. If you're in Assault, yes. It's good. But then, you also need to weigh it against Fearless, Eternal Warrior, etc. So not go-to, but highly, highly likely to come up.

Strategic:

1. All units have Move Through Cover and Stealth(Ruins). Not terrible, but as above, giving out Move Through Cover is easy to get if you really want it. Army-wide Stealth is pretty rad, though, so you might take it a lot just for that.
2. First turn is Night Fight and your dudes have Night Vision. First turn Warlord traits do nothing, and Night Vision does even less.
3. Warlord and 3 non-vehicle units have Infiltrate. See above.
4. Reserve manipulation. Goodness again depends on your number of reserves, but overall good. Note: statistically this is better than the Necron one, since 3+ rerolling is better than 2+, but the Necron one also helps you delay if you want the -1. Both are good in their own ways.
5. Enemy has a -1 to Reserve Rolls. Read above, but replace "your" with "the enemy's". Good depending on your opponent's level of reserves.
6. d3 Pinning tests on the enemy's first turn. As #2 and #3 here, can't use this.

Personal:

1. Warlord has Counter Attack. Hahaha no.
2. Warlord has Furious Charge. See #1. I mean, for both, I'm sure you can find a situation where getting +1S or an extra attack might be useful, but for the most part you're never going to pick this over other stuff.
3. Warlord has Outflank. You can't choose to go into Outflank reserve unless you have it before the game starts, so this is 100% useless.
4. +1VP per character he kills in a challenge. Guess. (Hint, it's really bad)
5. Warlord has FNP. RP is better in every way, every time.
6. Fearless and IWND. Fearless for a blob is good, IWND is nice but hopefully you won't need it. Still, Fearless is one of the best USRs in the game and if you switched away from Zealot and need to stay in combat, this is your guy.

Again, not everything in black is going to come up, and in fact some of them suck. But, there's always fringe cases, and having them is better than not having them.

In most games, you'll likely jump to one of the Reserve traits on turn 2 (either to deny the opponent or to boost your own), and then go to reroll 1s in shooting for most of the game unless you need a buff like Fearless, Charge distance, or Stealth.

As was brought to me by another poster, the strength isn't that any of these Traits wins the game by themselves, the strength comes from having the one you need for the right situation. You're almost never going to need to force your opponent to discard a card, but it might suddenly let you win by 1 point in a game. And you'll be glad you had it then.

The Robot, the Myth, the Legend

Zahndrekh's power comes from planning and thinking ahead. List creation with Allies can take Counter Tactics from a nice boost to something that shapes your army. Looking at the next turn and picking the right Trait can tip the scales in your favor, even if it's only a little bit. But a little bit might be exactly what you need.

And of course, this isn't taking into account the fun things you can do if you have Obyron, the amount of board control and mobility the two of them can bring together is pretty crazy. Overall, Zahndrekh is an amazing HQ, probably the best in the book if you use him right.

However, there is the very real chance that some of these traits will never come up, and he just sits on Command #5 all game for the rerolls. Other Characters have strengths that you can rely on. Orikan's rerolls and powerful Assault weapon are always going to be useful. Szeras' Eldritch Lance is always going to be good for something. Anrakyr will always make a squad of Immortals a hero squad. You can plan an army around these, while you can never plan for Zahndrekh picking Furious Charge to win you the game.

Flexibility can win games. But so can a kitted out Overlord with an Artifact. Figure out what your playstyle is and what you want your army wants to do. Zahndrekh can slot into any Necron army, period, but occasionally the right tool for what you want to do might already exist in another HQ choice.