For a 4-color deck, this deck really plays a lot of Green and White sources. That's because... surprise! This isn't really a 4-color deck. It's a Green/White deck splashing two colors. If this seems strange, take a look at the decklist again. In the maindeck, there are a total of 4 Blue cards: the 4 copies of
Saheeli Rai
. There are also only 5 Red cards: the
Saheeli Rai
s again, and
Kiki-Jiki, Mirror Breaker
. As a lot of the mana sources make "rainbow" mana, we can afford to skimp a bit on Blue and Red mana. We play the 3 on-color Red shocklands so that we can play a Kiki-Jiki if we don't have a Birds or a Cobra, and we only play 2 Blue shocklands because
Oath of Nissa
helps cast Saheeli.
The
Horizon Canopy
s are there because this deck can run out of steam in the lategame, and having lands that turn into cantrips is nice. They can also easily enable Revolt for
Renegade Rallier
, and Rallier can also bring them back if you need card draw. Try not to tap them for mana more than you need to, though; your lands can deal a lot of damage to you very quickly.
Q: But Pieguy396! Why is there a basic
Island
?
A: So
Blood Moon
and
Ghost Quarter
can't cut us off Blue. It's optional, though, so if you don't like it, feel free to play another basic
Forest
Q: But Pieguy396! Why don't you play
Hallowed Fountain
?
A: Because it's terrible. Green is much more central to the deck than White, and we almost never need to fetch a shockland specifically for Blue mana. This deck's manabase can also be extremely painful, so cutting even 1 shockland can make a world of difference.