Underworld Connections

Flying Vigilance (Attacking doesn't cause this creature to tap.)

Other Merfolk get +1/+1 and have islandwalk. (They can't be blocked as long as defending player controls an Island.)

Other Zombie creatures have swampwalk. (They can't be blocked as long as defending player controls a Swamp.) Other Zombies have "B: Regenerate this permanent."

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

As long as Gaea's Liege isn't attacking, its power and toughness are each equal to the number of Forests you control. As long as Gaea's Liege is attacking, its power and toughness are each equal to the number of Forests defending player controls. T: Target land becomes a Forest until this creature leaves the battlefield.

The owner of target permanent shuffles it into their library, then reveals the top card of their library. If it's a permanent card, they put it onto the battlefield.

T: Add one mana of any color in your commander's color identity. Sacrifice this artifact: Draw a card.

T: Add C. 4, T: Target creature can't be blocked this turn.