Consider that Murderous Cut cannot prevent a creature like Siege Rhino from triggering its ability when it enters the battlefield, it cannot kill a Planeswalker, and it cannot stop an instant or sorcery
To be honest, there should be another way of getting Lux out as well, though
As you can see there are plenty of red and red-leaning cards if you feel like one combat per turn is just not enough
Promos (P) Promotional cards - like the aforementioned Lightning Bolt from MagicFest - can come from events, prereleases, special products, store promos, conventions, Secret Lair drops, and various other places where Wizards know we players are willing to pay top dollar for them
"If only I could go back in time I would spend all my money and buy 10 Tarmogoyf when it was first released, I would be rich now"