They won't stop the creature from entering the battlefield attacking
One of the best decisions you can make before a Magic tournament is to have a plan for how to sideboard against the majority of the decks you intend to play against as well as a general idea for those you don't expect at all
Instead, were going to talk about one-drops that are very good in green decks in particular
Marath requires two things to do more than break even in value, however
Otter Limits Creature (21) Bria, Riptide Rogue Mockingbird Alania, Divergent Storm Thieving Otter x3 Bellowing Crier x3 Waterspout Warden x3 Alania's Pathmaker x3 Coruscation Mage x2 Quaketusk Boar x2 Stormcatch Mentor x2 Instant (5) Flame Lash x3 Rabid Gnaw x2 Sorcery (4) Enchantment (2) Artifact (1) Land (27) Swiftwater Cliffs x4 Island x11 Mountain x12 Hmm wonder what Otter Limits could be about
If it dies, youll return it to the battlefield as Edgar Markov's Coffin and makes 1/1 vampires, and later youll get Edgar back