Goblin King

Other Goblins get +1/+1 and have mountainwalk.

Foundry Street Denizen

Whenever another red creature you control enters, Foundry Street Denizen gets +1/+0 until end of turn.

Create two 1/1 red Goblin creature tokens.

Goblin spells you cast cost {1} less to cast.
Goblins you control have haste.

When Goblin Instigator enters, create a 1/1 red Goblin creature token.

Other Goblin creatures you control get +1/+1.
{T}: Regenerate another target Goblin.

When Sling-Gang Lieutenant enters, create two 1/1 red Goblin creature tokens.
Sacrifice a Goblin: Target player loses 1 life and you gain 1 life.