Perhaps the best way to keep an odd number of cards in hand are abilities that let you draw
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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
But even treating this as a 4-mana 3/2 that draws you a card sounds really good, and you can obviously divide up when you cast the two halves to make it feel even better and if you always have the mana available when it dies, it will just keep coming back When it has a big enough friend around, it is going to be an intimidating attacker on any board and that alone is enough for the Ruiner to be relevant almost all game long
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
Product Details Trance At the beginning of combat on your turn, mill two cards