I was playing brawl and my opponent had a Lilah, Undefeated Slickshot in play and cast and resolved a multicolored instant, Quandrix Command. Lilah then plotted the Quandrix Command and it showed it in exile as costing 0. Then, on my turn, I cast some spells and my opponent responded by casting Quandrix Command for free from plot, something that should not be possible as plot only allows it to be cast as a sorcery. I don't think there was anything in play that should affect this. This occurred in a Riku of Many Paths brawl deck and Riku was in play and some cards were exiled to Riku's ability as well.