Modern

Eldrazi, or no Eldrazi?

The Eldrazi package adds a ton of power to the deck. Turn two Thought-Knot Seer, while uncommon for this particular deck, is still a very powerful play in Modern. The other Eldrazi also add more value to your deck, often serving as 2 for 1s or better. However, playing with these powerful Eldrazi come at a cost- since they specifically require colorless mana to cast or use, they add a third color to the deck. Therefore, since fetch lands cannot be used in the deck (nonbo with Leonin Arbiter), you are required to play with a suboptimal mana base that can, at times, cost you the game. Overall, I personally believe that it is worth the cost to play the Eldrazi builds over the tradition Mono-White builds in Modern, as it adds a ton of power and enjoyment to the deck.

Basic Sideboarding:

Right now, Modern is a very diverse format, making optimal sideboarding difficult, but essential nonetheless. Currently, there are a few essential sideboard options for all lists (regardless of splashes)- Rest in Peace and Stony Silence. Both of these cards hurt combo and aggro decks, helping you not die in the early turns. The remaining slots are often populated with value creatures or other hate cards to combat faster decks (like Burn hate). The lists above have basic sideboards to start with, but ultimately it is best to tune your sideboard based on your local meta.

Splashing colors:

While splashing is not as easy in Modern as it is in Legacy due to the lack of painless duals, splashing in Modern is very beneficial, due to it expanding your options outside of white, which is much more limited in Modern compared to legacy. In fact, unlike Legacy, there are versions of the deck splashing every color (even blue!). There are currently not any three color versions in Modern (besides Eldrazi and Taxes), and probably for good reason (fetches are a nonbo with Leonin Arbiter).