When she's on the other side, he telekinetically closes and locks it.

Then he turns toward the gate. Resources: Metalminds charged with implausible amounts of everything. Special mention to luck. Hemalurgic spikes making him stronger and faster. (The ones increasing Allomantic power are completely irrelevant here.) And a plentiful supply of atium. If his theory about why Allomancy doesn't do anything in Fairyland is correct, burning atium should work. And anyone burning atium is all but unstoppable.

He walks through.