The Competitive Sealed League lasts for 5 matches and typically features higher skilled players due to the top-heavy prize structure - winning all or most of your rounds provides a lucrative prize, with the downside of no prizes being offered to those who win less than 60% of their matches
For decks with three or more colors, where you might only be able to afford a small number of MDFCs since you'll need most of your lands to either be basics (for ramping / tutoring purposes) or tap for multiple colors of mana, the best MDFCs are Bala Ged Recovery (seriously, if you have green mana in your deck, play this card), Valakut Awakening, Hagra Mauling, and Ondu Inversion, along with the mythic cycle, which is almost always good if you can afford another land that only taps for a single color of mana
Stormsplitter This otter wizard is a Timmy card that I want to prove is busted
When Hidetsugu and Kairi dies, exile the top card of your library
Plaxcaster Frogling Plaxcaster Frogling is a solid role-player for +1/+1 counter decks, though Id pass on it digitally (graft triggers on every creature that enters, including your opponents)