I get a lot of questions about Tireless Tracker when it comes to Pioneer, or like, what my wish list would be for Historic/Explorer and what would be on it. Well, now we have Tracker in Explorer, so it's not a hypothetical anymore. Tracker is at its best in a deck that is built with it in mind, which isn't to say that it needs to be a specific archetype, but more that it needs to exist at a certain part of a curve and for a deck that is geared to utilize it.
Landfall abilities necessitate having a slightly higher than normal land count, which is funny because they usually are proactive abilities, like Kazandu Mammoth or Steppe Lynx. A Boros aggro deck doesn't usually run 26 lands or whatever they did back in the original Zendikar days, but when you have stuff as powerful as Steppe Lynx and Plated Geopede, you want to get those triggers as much as possible. This isn't the hugest problem for Tireless Tracker, because if you have too many lands, then you'll also have clue tokens to spend your mana on. But in the draws that don't have Tracker, you'll find yourself getting flooded too much.
The other thing that Tracker wants is cheap spells to go with it. First of all, your ideal plan is to cast Tracker on turn four and make your fourth land drop. A one mana spell to follow up with is excellent, like say a Thoughtseize to make sure the opponent can't untap and kill it, or a Fatal Push to keep your life total high and utilize your extra card advantage. Bloodchief's Thirst and even Shivan Fire are nice, because they are solid when you're flooded or when you're tight on mana. Additionally, though, all the cards that you draw off of a Tracker cost you an additional two mana, so if you want to be able to actually cast them, you want them to be cheap. I think the other factor here is that Tracker is a pretty slow card and you need to set it up, so you want to make the board as clear as possible before landing it, kind of like a Planeswalker. It doesn't want to be forced to play defense and it doesn't attack and block especially well right out of the gates, so keeping up on tempo is really important, and then let the Tracker take over the game.
So then, we want a deck with lots of lands and lots of cheap spells, sounds like a recipe for mana flooding. You're going to want to play cards that mitigate your land flood as much as possible, like creature lands, cycling lands, and even Jegantha. I like Tenacious Underdog as a mana sink/early play, and Valki as a card that fits the program but can be a good late game topdeck.
What makes Riveteers Charm so good in a deck with Tracker is that it's a removal spell, so that's obviously good at keeping pressure off yourself, but it also excels in a deck with cheap spells and a high land count. Your best three card exile for a Charm is like, removal spell, land, threat, and if your deck is set up with Tracker in mind, then you're likely to be able to cast all of it. I think there's something good here, mixing Tracker with Charm and all kinds of cheap stuff, so that you can keep the cards flowing and out-value people while keeping your curve super low and not getting tempo'd out.
Witherbloom Command is another card that works well with high land counts that can do some work for us. Now that Elvish Mystic is in the format, more ways to pop off little guys for value seems like it's useful, and Witch's Oven is always a problem.
I've gotta say, in the first little while playing with Tracker, I have been impressed. Not floored, but it's better than I had anticipated. You have to get away from the typical Chandra/Fable/Trespasser Rakdos decks that are all over Explorer, so nothing is very set in stone yet, but I think something's there.
~
Just wanted to get something down real quick about Tracker, I'll know more soon after more testing. If you're planning on trying Tracker out, those are the things I suggest. Again, not 100% sold that it's the best thing, but I think there's a re-tooling of the current Jund deck that can make it really strong. Thanks for reading.