The Ozolith

Whenever a creature you control leaves the battlefield, if it had counters on it, put those counters on The Ozolith.
At the beginning of combat on your turn, if The Ozolith has counters on it, you may move all counters from The Ozolith onto target creature.

Casal, Pathbreaker Owlbear

Vigilance, trample
When this creature transforms into Casal, Pathbreaker Owlbear, other legendary creatures you control get +2/+2 and gain trample until end of turn.
At the beginning of your upkeep, transform Casal.

Casal, Lurkwood Pathfinder

Vigilance
When Casal enters, search your library for a Forest card, put it onto the battlefield tapped, then shuffle.
Whenever Casal attacks, you may pay {1}{G}. If you do, transform her.

Casal, Lurkwood Pathfinder // Casal, Pathbreaker Owlbear

Trelasarra, Moon Dancer

Whenever you gain life, put a +1/+1 counter on Trelasarra and scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Mirror Gallery

Mirror Box

The "legend rule" doesn't apply to permanents you control.
Each legendary creature you control gets +1/+1.
Each nontoken creature you control gets +1/+1 for each other creature you control with the same name as that creature.

Heroic Intervention

Permanents you control gain hexproof and indestructible until end of turn.

Hero's Blade

Equipped creature gets +3/+2.
Whenever a legendary creature you control enters, you may attach this Equipment to it.
Equip {4} ({4}: Attach to target creature you control. Equip only as a sorcery.)

Frodo Baggins

Whenever Frodo Baggins or another legendary creature you control enters, the Ring tempts you.
As long as Frodo Baggins is your Ring-bearer, it must be blocked if able.

Legolas Greenleaf

Reach
Legolas can't be blocked by creatures with power 2 or less.
Whenever another legendary creature you control enters, put a +1/+1 counter on Legolas.
Whenever Legolas deals combat damage to a player, draw a card.

Heliod, Sun-Crowned

Indestructible
As long as your devotion to white is less than five, Heliod isn't a creature.
Whenever you gain life, put a +1/+1 counter on target creature or enchantment you control.
{1}{W}: Another target creature gains lifelink until end of turn.

Mirari's Wake

Creatures you control get +1/+1.
Whenever you tap a land for mana, add one mana of any type that land produced.

Tolsimir, Friend to Wolves

When Tolsimir enters, create Voja, Friend to Elves, a legendary 3/3 green and white Wolf creature token.
Whenever a Wolf you control enters, you gain 3 life and that creature fights up to one target creature you don't control.