Maester Seymour

At the beginning of combat on your turn, put a number of +1/+1 counters equal to Maester Seymour's power on another target creature you control.
{3}{G}{G}: Monstrosity X, where X is the number of counters among creatures you control. (If this creature isn't monstrous, put X +1/+1 counters on it and it becomes monstrous.)

Werewolf Pack Leader

Pack tactics — Whenever this creature attacks, if you attacked with creatures with total power 6 or greater this combat, draw a card.
{3}{G}: Until end of turn, this creature has base power and toughness 5/3, gains trample, and isn't a Human.

Burakos, Party Leader

Burakos is also a Cleric, Rogue, Warrior, and Wizard.
Whenever Burakos attacks, defending player loses X life and you create X Treasure tokens, where X is the number of creatures in your party.
Choose a Background (You can have a Background as a second commander.)

Spider-Rex, Daring Dino

Reach, trample
Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)

Swamp

Runed Stalactite

Equipped creature gets +1/+1 and is every creature type.
Equip {2}

Stonework Packbeast

Stonework Packbeast is also a Cleric, Rogue, Warrior, and Wizard.
{2}: Add one mana of any color.

Diligent Zookeeper

Each non-Human creature you control gets +1/+1 for each of its creature types, to a maximum of 10.

Yargle and Multani

Tajuru Paragon

Tajuru Paragon is also a Cleric, Rogue, Warrior, and Wizard.
Kicker {3}
When this creature enters, if it was kicked, reveal the top six cards of your library. You may put a card that shares a creature type with it from among them into your hand. Put the rest on the bottom of your library in a random order.

Tyvar, the Pummeler

Tap another untapped creature you control: Tyvar gains indestructible until end of turn. Tap it.
{3}{G}{G}: Creatures you control get +X/+X until end of turn, where X is the greatest power among creatures you control.

Varolz, the Scar-Striped

Each creature card in your graveyard has scavenge. The scavenge cost is equal to its mana cost. (Exile a creature card from your graveyard and pay its mana cost: Put a number of +1/+1 counters equal to that card's power on target creature. Scavenge only as a sorcery.)
Sacrifice another creature: Regenerate Varolz.

Hardy Outlander

Commander creatures you own have "Whenever this creature attacks a player, if no opponent has more life than that player, another target creature you control gets +X/+X until end of turn, where X is this creature's power."

Life's Legacy

As an additional cost to cast this spell, sacrifice a creature.
Draw cards equal to the sacrificed creature's power.

Forest

Momentous Fall

As an additional cost to cast this spell, sacrifice a creature.
You draw cards equal to the sacrificed creature's power, then you gain life equal to its toughness.

Command Tower

{T}: Add one mana of any color in your commander's color identity.

Agatha's Soul Cauldron

You may spend mana as though it were mana of any color to activate abilities of creatures you control.
Creatures you control with +1/+1 counters on them have all activated abilities of all creature cards exiled with Agatha's Soul Cauldron.
{T}: Exile target card from a graveyard. When a creature card is exiled this way, put a +1/+1 counter on target creature you control.

Embiggen

Until end of turn, target non-Brushwagg creature gets +1/+1 for each supertype, card type, and subtype it has.

Veteran Adventurer

Veteran Adventurer is also a Cleric, Rogue, Warrior, and Wizard.
This spell costs {1} less to cast for each creature in your party.
Vigilance

Shadowheart, Dark Justiciar

{1}{B}, {T}, Sacrifice another creature: Draw X cards, where X is that creature's power.
Choose a Background (You can have a Background as a second commander.)