Maybe I wasn't let in on it, but last I checked it didn't take 6 Pokemon to catch just one legendary, but again it could just be me. False Swipe is not a necessary move when capturing legendary Pokemon. Yes having it at one HP is helpful, but normal attacking moves are just as useful. Mainly due to the fact that False Swipe, being a Normal type move, can not affect some legendary Pokemon and resistant to others. Go try False Swiping a Landorus, let me know how that works. Sleep inducing moves aren't all that reliable. Mainly being that the Pokemon can wake up from it. This means that you'll have to keep using it over and over. This makes T-Wave an okay choice. Last I check ain't no legendary Pokemon shaking off paralysis unless it's got a berry or some move that clears status effects. Jolteon is good due to its high speed, it's ability to inflict paralysis, and it's got a good Sp.Atk stat for some damage. Slyveon is good due to it's impressive defensive capabilities, recovery options, and great typing. So maybe I left out Synchronize, but the question didn't say that it was for competitive purposes, so if the user is just catching them to have them, Then nature doesn't matter.