In this entry I listed a number of guidelines I follow when deciding which cards I want in my cubes.
Here’s a PDF you can open in a new window to look at the part of my list I’m taking about while reading:
And here’s a link to an explanation of the shortcuts I use in that list, if you need it.
Eland Umbra is just more special than Hyena Umbra, being one of very few auras boosting toughness, but not power, and still being playable. (Chosen by Heliod is another.) I use Umbras only in White and Blue, a common and an uncommon in each color, because the green Umbras do not convince me. I like these cards simple and elegant, with the ability to save the creature from destruction being an important feature. Drawing cards or untapping lands distracts too much from that – if I want that effect, I use an aura which focusses on it, like Keen Sense. The more generic green choices do not play well or are too powerful.
I’d love to simply mirror Bad Moon, but Crusade is a little worse, and Honor of the Pure a little better. So, having to choose, I give the stronger pump spell to White, which tends to be a lot friendlier to creatures than Black overall.
Selecting enchantments which are strong enough to matter, but not too strong if an opponent can not remove them is tricky, but especially important, since only White and Green are really well suited to deal with enchantments, and Red and Black have practically no way. Auras, obviously, can be dealt with indirectly, but global enchantments can not. One of those which makes sense to me as a high-end play is Martyr’s Bond. It obviously has a large impact, but is not an auto-win, and there might be ways to play around it.
Auras which aren’t very cheap need to be powerful to offset their inherent disadvantage, but still should not win a game too fast on their own. That’s why I got rid of Armored Ascension, which is somehow acceptable in a two-color deck (but less interesting and balanced than Serra’s Embrace) – in a monocolored deck, however, it will often kill an opponent in two swings out of nowhere. Since the whole point of such a card is to reward a player for being as monocolored as possible, it makes no sense to keep it around for other environments.
Buyback has been cited by WotC as causing repetitive play issues, but is essentially a variant of a permanent with an activated ability which sits in a player’s hand. That makes it harder to interact with, but certainly not more repetitive. I have one or two buyback spells in each color, because they are both useful as normal, cheap spells, or mana sinks in the lategame, and are thus excellent fits for some environments (they go very nicely with landfall, for example).
I already explained in my former entry how cantrips and cards with cycling help to thin out decks and fill the graveyard. Instants and sorceries with these mechanics can also serve to increase the ratio of these card types in decks while providing compensation for a lower creature count – there’s always some tension here with an instery theme, and these cards help to alleviate it.
While reliable removal is important in a cube, I cut the most efficient versions from my pool (among more general reasons, to help auras a little), especially outside of Black, which is supposed to be the strongest in that aspect to compensate for its deficiencies in others. So, no Swords to Plowshares, Path to Exile, Lightning Bolt or Flame Slash. White, however, still has a lot of conditional (like Condemn) or undoable (like Journey to Nowhere) removal.
Flashback is another mechanic supporting a graveyard theme. Since there are several of those, I do not need high numbers in each.
There are roughly a million Wrath of God variants, but the original is still the best – I do not at all like the idea that regenerating should save a creature from the ultimate creature removal spell, and four mana is fine in limited, since breaking that card’s symmetry needs a lot more work here than in constructed. Planar Cleansing is a good companion/alternative, sitting in a clearly distinct mana slot, and having a clearly broader effect (although, unfortunately, it allows for regeneration).