Twilight Drover has at least one +1/+1 counter on it.
({2} magic symbol) ({W} magic symbol) available.
Steps
Activate Twilight Drover by paying ({2} magic symbol) ({W} magic symbol) and removing a +1/+1 counter from it, creating four 1/1 Spirit creature tokens with flying.
Activate Phyrexian Altar three times by sacrificing three Spirits, adding ({2} magic symbol) ({W} magic symbol) .
When the Spirits die, Twilight Drover triggers three times, putting six +1/+1 counters on itself.