Ruby Crystal

Arsenal(You may cast this card from your sideboard.)
Armed creature gets +0/+1.
Arm {c}({c}: Attach to target legendary creature you
control as a sorcery. As long as this ability is on the
stack, your opponents can't cast spells or activate
abilities.Whenever a legendary creature you control
enters the battlefield, you may arm that creature
as an instant without paying this card arm cost.)