Whenever another legendary permanent you control enters, put a +1/+1 counter on Yoshimaru.
Partner (You can have two commanders if both have partner.)

+2: Creatures you control with flying get +1/+1 until end of turn.
−3: Create a 4/4 white Angel creature token with flying and vigilance.
−6: You get an emblem with "If you control a creature, damage that would reduce your life total to less than 1 reduces it to 1 instead."

Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)
Sliver spells you cast have cascade.

+2: Ugin deals 3 damage to any target.
−X: Exile each permanent with mana value X or less that's one or more colors.
−10: You gain 7 life, draw seven cards, then put up to seven permanent cards from your hand onto the battlefield.

Eminence — As long as The Ur-Dragon is in the command zone or on the battlefield, other Dragon spells you cast cost less to cast.
Flying
Whenever one or more Dragons you control attack, draw that many cards, then you may put a permanent card from your hand onto the battlefield.