Cheapest priced copy (The List): $0.35 at Card Kingdom, near mint, their price list as of .
Tower Above 
Sorcery · Uncommon · Shadowmoor · #131
({2/G} can be paid with any two mana or with {G}. This card's mana value is 6.)
Until end of turn, target creature gets +4/+4 and gains trample, wither, and "When this creature attacks, target creature blocks it this turn if able." (It deals damage to creatures in the form of -1/-1 counters.)
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
2 printings · $0.35 to $1.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| The List | SHM-131 | Uncommon | $0.35 | — |
| Shadowmoor | 131 | Uncommon | $0.35 | $1.99 |
5 rulings from Wizards of the Coast
- 1 May 2008A card with a monocolored hybrid mana symbol in its mana cost is each of the colors that appears in its mana cost, regardless of what mana was spent to cast it. Thus, Tower Above is green even if you spend six white mana to cast it.
- 1 May 2008A card with monocolored hybrid mana symbols in its mana cost has a mana value equal to the highest possible cost it could be cast for. Its mana value never changes. Thus, Tower Above has a mana value of 6, even if you spend {G}{G}{G} to cast it.
- 1 May 2008If an effect reduces the cost to cast a spell by an amount of generic mana, it applies to a monocolored hybrid spell only if you've chosen a method of paying for it that includes generic mana.
- 1 May 2008If a cost includes more than one monocolored hybrid mana symbol, you can choose a different way to pay for each symbol. For example, you can pay for Tower Above by spending {G}{G}{G}, {2}{G}{G}, {4}{G}, or {6}.
- 1 May 2008When the creature affected by Tower Above attacks, you can target any creature on the battlefield with the triggered ability. However, if the creature you target can't block the creature affected by Tower Above (for example, because the attacking creature has flying and the other one doesn't, or because both creatures are controlled by the same player), the triggered ability does nothing. In that case, the creature you targeted is free to block whichever creature its controller chooses, or block no creatures at all.