Walking Ballista [Aether Revolt] Desert you can't be attacked except

you can't be attacked except by creatures with flying and/or islandwalk

Set: Mirrodin Type: Artifact — Equipment Rarity: Rare Cost: {2} Equipped creature gets +2/+2

"I'll have my revenge if I have to call on every force from above and below

Set: New Phyrexia Type: Artifact Creature — Phyrexian Horror Rarity: Rare Cost: {2} {U/P}: Change a target of target spell or ability to Spellskite

Walking Ballista [Aether Revolt] Desert you can't be attacked exceptSet: Aether Revolt Type: Artifact Creature Construct Rarity: Rare Cost: {X}{X} Walking Ballista enters the battlefield with X +1 +1 counters on it. {4}: Put a +1 +1 counter on Walking Ballista. Remove a +1 +1 counter from Walking Ballista: It deals 1 damage to any target.