Forum:Question About Machina Fortress

Hello, I was wondering if you can discard machine monsters equal to level 8 or higher to receive machina fortress during your battle phase? Like lets say you attacked then you opponent uses mirror force. Can you then discard the machines to revive machina fortress or do you have to wait for Main phase 2? Also, is machina fortress first effect negated by skill drain? It says "When this card is destroyed and sent to the graveyard, select and destroy 1 card your opponent controls." Thanks