In order to cast your Signature Spell, you need to have your Planeswalker (Oathbreaker) on the battlefield, this means that lower cost Planeswalkers will be played more often so that you can cast your Signature Spell sooner
Look for creatures that compliment your commander by either helping you cast them, or playing into their goals
Frankly, six mana for a 5/5 Flying Angel and an extra permanent with mana value four or greater is ok, but not great
Card Set(s) -THE AZURE SEAS SEVEN- [OP14-EB04] CARD VIEW OP14-040 | L | LEADER Jinbe Attribute Strike Block icon 4 Type Fish-Man/The Seven Warlords of the Sea/The Sun Pirates Effect [Activate: Main] You may trash 1 card from your hand: Give up to 2 rested DON
Token creatures can be permanently removed more easily than other creatures since they die to bounce spells
Provided you can crew or saddle with it, or get in for a free attack, you can turn on the extra mana tap