Barricade Breaker

Improvise (Your artifacts can help cast this spell. Each artifact you tap after you're done activating mana abilities pays for {1}.)
This creature attacks each combat if able.

Juggernaut

This creature attacks each combat if able.
This creature can't be blocked by Walls.

Graaz, Unstoppable Juggernaut

Juggernauts you control attack each combat if able.
Juggernauts you control can't be blocked by Walls.
Other creatures you control have base power and toughness 5/3 and are Juggernauts in addition to their other creature types.

Ramroller

This creature attacks each combat if able.
This creature gets +2/+0 as long as you control another artifact.