The Evoke Elementals like Solitude
It can fetch answers or combo pieces like Rest in Peace or Phyrexian Unlife, so you can adjust your plan based on what the game demands
However, you can consider playing fewer than four copies of a card if: It gets worse in multiples (such as legendary creatures) It's only useful against certain matchups It's a win condition, and your control deck will have time to dig through the deck and find it You're stuck choosing between two cards which have equally strong, similar, but slightly different effects (you could play two of each) It's a slightly worse version of a card you have four copies of already, and you're including it because you want even more of that effect
Her two abilities are Trance which lets you send the top two cards from your deck to the graveyard (called milling) and in return, Terra gains Flying, making her much more difficult to block
You just have to hope that nobody else casts a world enchantment of their own to get rid of it
Perhaps the best way to keep an odd number of cards in hand are abilities that let you draw