Blood Begets Blood...

Kicker {b}{b}{r}
Target creature you control fights target creature
an opponent controls. Then, if one of those
creatures is destroyed after damage calculation,
the owner of that card may have another target creature they control fight the surviving creature. Continue this process until a player chooses not
to retaliate, or a creature is not destroyed after
damage, or one player controls no creatures. If
this card was kicked, replace the word 'may' with
'must'.