It could be a -1 from Jace, the Mind Sculptor, it could be a Ravenous Chupacabra, it could just a be a Doom Blade
If you play something like Elves, Goblins, Humans, or Merfolk, you can fill your deck with 30 creatures of the right type and never worry about your mana curve because these creatures exist at all reasonable points in the curve, but if you ever play 30 Giants in a deck, then the average converted mana cost will be five and you will lose most games without ever casting a spell
Shipwreck Marsh Rarity: Rare TYPE: Land SUBTYPE: - CMC: 0 Mana cost: USD: $7.49 EUR: 5.03 TIX: 0.11 EDHREC RANK: 231 This land enters tapped unless you control two or more other lands
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It's just a little bit more of a glass cannon that I would expect but then again, that sort of makes sense in a deck based around 50/50 chances of winning