Heronblade Elite

Vigilance
Whenever another Human enters the battlefield under your control, put a +1/+1 counter on Heronblade Elite.
{T}: Add X mana of any one color, where X is Heronblade Elite's power.

Ilysian Caryatid

{T}: Add one mana of any color. If you control a creature with power 4 or greater, add two mana of any one color instead.

Avacyn's Pilgrim

Bess, Soul Nourisher

Whenever one or more other creatures with base power and toughness 1/1 enter the battlefield under your control, put a +1/+1 counter on Bess, Soul Nourisher.
Whenever Bess attacks, each other creature you control with base power and toughness 1/1 gets +X/+X until end of turn, where X is the number of +1/+1 counters on Bess.

Arcane Signet

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

Arbor Elf