Opalescence

Each other non-Aura enchantment is a creature in addition to its other types and has base power and base toughness each equal to its mana value.

Hidden Spider

When an opponent casts a creature spell with flying, if Hidden Spider is an enchantment, Hidden Spider becomes a 3/5 Spider creature with reach. (It can block creatures with flying.)

Opal Caryatid

When an opponent casts a creature spell, if Opal Caryatid is an enchantment, Opal Caryatid becomes a 2/2 Soldier creature.

Hidden Ancients

When an opponent casts an enchantment spell, if Hidden Ancients is an enchantment, Hidden Ancients becomes a 5/5 Treefolk creature.

Lurking Skirge

When a creature is put into an opponent's graveyard from the battlefield, if Lurking Skirge is an enchantment, Lurking Skirge becomes a 3/2 Phyrexian Imp creature with flying.

Myrkul, Lord of Bones

As long as your life total is less than or equal to half your starting life total, Myrkul, Lord of Bones has indestructible.
Whenever another nontoken creature you control dies, you may exile it. If you do, create a token that's a copy of that card, except it's an enchantment and loses all other card types.

Opal Titan

When an opponent casts a creature spell, if Opal Titan is an enchantment, Opal Titan becomes a 4/4 Giant creature with protection from each of that spell's colors.

Vine Dryad

You may exile a green card from your hand rather than pay this spell's mana cost.
Flash
Forestwalk (This creature can't be blocked as long as defending player controls a Forest.)

Hidden Gibbons

When an opponent casts an instant spell, if Hidden Gibbons is an enchantment, Hidden Gibbons becomes a 4/4 Ape creature.

Hidden Guerrillas

When an opponent casts an artifact spell, if Hidden Guerrillas is an enchantment, Hidden Guerrillas becomes a 5/3 Soldier creature with trample.

Hidden Predators

When an opponent controls a creature with power 4 or greater, if Hidden Predators is an enchantment, Hidden Predators becomes a 4/4 Beast creature.

Hidden Herd

When an opponent plays a nonbasic land, if Hidden Herd is an enchantment, Hidden Herd becomes a 3/3 Beast creature.

Opal Champion

When an opponent casts a creature spell, if Opal Champion is an enchantment, Opal Champion becomes a 3/3 Knight creature with first strike.

Opal Archangel

When an opponent casts a creature spell, if Opal Archangel is an enchantment, Opal Archangel becomes a 5/5 Angel creature with flying and vigilance.

Hidden Stag

Whenever an opponent plays a land, if Hidden Stag is an enchantment, Hidden Stag becomes a 3/2 Elk Beast creature.
Whenever you play a land, if Hidden Stag is a creature, Hidden Stag becomes an enchantment.

Opal Guardian

When an opponent casts a creature spell, if Opal Guardian is an enchantment, Opal Guardian becomes a 3/4 Gargoyle creature with flying and protection from red.

Opal Acrolith

Whenever an opponent casts a creature spell, if Opal Acrolith is an enchantment, Opal Acrolith becomes a 2/4 Soldier creature.
{0}: Opal Acrolith becomes an enchantment.

Opal Gargoyle

When an opponent casts a creature spell, if Opal Gargoyle is an enchantment, Opal Gargoyle becomes a 2/2 Gargoyle creature with flying.