({BR} magic symbol) ({BR} magic symbol) ({BR} magic symbol) , minus ({BR} magic symbol) for each +1/+1 counter on
Runaway Steam-Kin available.
Steps
Activate
Phyrexian Altar by sacrificing
Undead Sprinter, adding ({BR} magic symbol) .
If
Runaway Steam-Kin has three or more +1/+1 counters on it, activate it by removing three +1/+1 counters from it, adding ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) .
Cast
Undead Sprinter from your graveyard by paying ({B} magic symbol) ({R} magic symbol) .
Runaway Steam-Kin triggers, putting a +1/+1 counter on it.