1) crew of 7 or 8 members (with 1 slug)
2) multiple systems you don't need to use
3) clone bay maxed out
4) teletransport maxed out
5) Reconstructive Teletransport augmentation installed
6) enemy ship big enough to send all boarding party in one room
Or you already start with 4 Lanius who can take out the air in two rooms and deal a lot more damage than a Mantis?
Why else do you think the Crystal B and the Mantis B & C are nerfed so much with their starting equipment?