Bloodform Horror

Bloodform Horror's power and toughness are
each equal to the total number of +1/+1 counters
among other creatures you control.
Whenever a player pays life to activate a spell or ability, put a +1/+1 counter on another target creature you control.
{t}, {b}, pay 4 life: Target player lose X life, where
X is the number of creatures you control with
counters on them.