One more trick to drop veil before you being shot by cannon at the boss area.the veil should be placed before the canoj strikes.by the time you were pushed and rejoin the mobs group the smoke activated at precise time.overall its faster than casting veil after (meaning once everyone has grouped.the smooe bomb takes couole of secs to explode and release smoke). Use slag to stun the mobs once they are trapped in the smoke prerimeter so you can utilize the smoke duration for offensive.