Delina, Wild Mage

Whenever Delina attacks, choose target creature you control, then roll a d20.
1—14 | Create a tapped and attacking token that's a copy of that creature, except it's not legendary and it has "At end of combat, exile this token."
15—20 | Create one of those tokens. You may roll again.

Day of Destiny

Legendary creatures you control get +2/+2.

Double Major

Copy target creature spell you control, except it isn't legendary if the spell is legendary. (A copy of a creature spell becomes a token.)

Blackblade Reforged

Equipped creature gets +1/+1 for each land you control.
Equip legendary creature {3}
Equip {7}

Join the Group

You may put a legendary creature card from your hand into the command zone. It's also your commander.

Champions of Archery

Reach
Commanders you control get +X/+0, where X is the number of commanders you control.

Champions of Archery // Join the Group

Avacyn's Memorial

Indestructible
Other legendary permanents you control have indestructible.

Champion's Helm

Equipped creature gets +2/+2.
As long as equipped creature is legendary, it has hexproof. (It can't be the target of spells or abilities your opponents control.)
Equip {1}

Arvad the Cursed

Deathtouch, lifelink
Other legendary creatures you control get +2/+2.

Bard Class

(Gain the next level as a sorcery to add its ability.)
Legendary creatures you control enter with an additional +1/+1 counter on them.
{R}{G}: Level 2
Legendary spells you cast cost {R}{G} less to cast. This effect reduces only the amount of colored mana you pay.
{3}{R}{G}: Level 3
Whenever you cast a legendary spell, exile the top two cards of your library. You may play them this turn.

Captain Sisay

{T}: Search your library for a legendary card, reveal that card, put it into your hand, then shuffle.