This deck you are having here is a board flood based one, you shouldn't need Piercing Rune. Maybe replacing it with something like wind blast will work better. You should consider putting the normal chimera (silver) in for more board control ability and popping your mammoth more consistently. Although tbh I think you should pull mammoth out. He probably will brick your hand and there is a lot of other options for a 3pp play, the cores for example.
About the muligan: you should probably aiming for hand of fate instead of flame destroyer.
Also, avoid doing owl -> evolve owl -> daria. It should be owl -> daria -> evolve owl. Only evolve owl first if you think your old hand have something worth playing (a flame destroyer or a chimera, for example).
Even with all that, imo the best daria deck is something that focus more in storms and going face. I even took owl out to put old Levi in with Clark (gold) to push lethal. Still that's a lot of gold and I think you should be ok with your current board-based playstyle.