Unexpected Allegiance

{ut}{2}{b/r}{b/r} All soldiers you control get +1/0
and gain first strike and vigilance. This effect costs X less to cast for every historic permanent you control (legendary spells, artifacts and saga spells are historic).
{b/r}{b/r}{b/r} Unexpected Allegiance becomes a
4/4 soldier with haste and vigilance until the
end of the turn.