We heard about these a while ago, but yesterdays preview stream finally gave us a proper look
And there are probably +1/+1 counters and even more kinds of counters in the set
Although this will not be a sideboard guide but more a how to play each matchup, I do have a short sideboard guide against most decks in Modern that you can find here
Thanks to Contender's enter the battlefield trigger, we are able to select the best Knight, Aura, Equipment, or legendary artifact card from the top five of our deck and add it to our hand
Tyranid Invasion is great early (since you usually have three opponents), Tyranid Prime is absolutely bonkers, one of the best cards in the deck, and Tyrant Guard is pretty good, offering protection to your board