({4} magic symbol) available in at least three different colors available.
Steps
Cast
Crystalline Crawler by paying ({4} magic symbol) , ensuring to spend at least three different colors of mana to cast it, causing
Crystalline Crawler to enter the battlefield with at least three +1/+1 counters on it.
When
Crystalline Crawler enters the battlefield,
Railway Brawler triggers, putting four +1/+1 counters on it.
Activate
Crystalline Crawler's first ability by removing all +1/+1 counters from it, adding ({W} magic symbol) ({U} magic symbol) ({B} magic symbol) ({R} magic symbol) ({G} magic symbol) and the remaining mana in any combination of color(s).