Cheapest priced copy (Journey into Nyx): $0.35 at Card Kingdom, near mint, their price list as of .
Oakheart Dryads 
Enchantment Creature — Nymph Dryad · 2/3 · Common · Journey into Nyx · #133
Constellation — Whenever this creature or another enchantment you control enters, target creature gets +1/+1 until end of turn.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Journey into Nyx | 133 | Common | $0.35 | $0.49 |
3 rulings from Wizards of the Coast
- 26 April 2014A constellation ability triggers whenever an enchantment enters the battlefield under your control for any reason. Enchantments with other card types, such as enchantment creatures, will also cause constellation abilities to trigger.
- 26 April 2014An Aura spell without bestow that has an illegal target when it tries to resolve won't resolve and will be put into its owner's graveyard. It won't enter the battlefield and constellation abilities won't trigger. An Aura spell with bestow won't be countered this way. It will revert to being an enchantment creature and resolve, entering the battlefield and triggering constellation abilities.
- 26 April 2014When an enchantment enters the battlefield under your control, each constellation ability of permanents you control will trigger. You can put these abilities on the stack in any order. The last ability you put on the stack will be the first one that resolves.