(MTR)-HKIA to Mongkok

From HKIA to Mongkok by metro, you need to make several transfers: take airport express to Tsing Yi, then transfer to Tung Chung Line to Lai King, then transfer to Tsuen Line to Mong Kok. Duration is about 50 minutes and ticket fare is HKD 68.
The last airport express is at 00:48, the last metro at Tsing Yi to Lai King is at 00:32; the last metro at Lai King to Mong Kok is at 00:37. If you hurry up, you can make it.

However, an easier way is by direct bus A21. Duration is about 40-50 minutesad ticket fare is HKD 33. The last schedule is at 24:00. If you cannot catch it, go to take the direct N21, which runs from 00:20 to 04:40. Good luck~