**For the record, most legendaries have a BST of 680, 600 or 580.**

Base 680 is generally what most of the main mascot legendaries have, including Ho-oh, Lugia, Yveltal etc.

The ones below are the ones under 650, and I've grouped them into their own categories, like the Legendary Birds, Lati Twins etc. since it's easier to read, and more easily identifiable that way.

Zapdos, Articuno, Moltres (Base 580)

- Mew (Base 600)

- Entei, Suicune, Raikou (Base 580)

- Celebi (Base 600)

- Regirock, Regice, Registeel (Base 580)

- Latios, Latias (Base 600)

- Jirachi (Base 600)

- Deoxys-D, A, S and N (Base 600)

- Azelf, Mesprit, Uxie (Base 580)

- Cresselia (Base 600)

- Darkrai (Base 600)

- Manaphy (Base 600)

- Phione (Debateable - base 480)

- Heatran (Base 600)

- Shaymin, Shaymin-S (Base 600)

- Victini (Base 600)

- Terrakion, Cobalion, Keldeo (Keldeo-Resolute as well), Virizion (Base 600)

- Thundurus, Tornadus, Thundurus-T, Tornadus-T (Base 580)

- Landorus, Landorus-T (Base 600)

- Meloetta (Both Aria and Pirouette forms) (Base 600)

- Genesect (Regardless of Drive or no Drive) (Base 600)

- Zygarde (Base 600)

- Diancie (Base 600)

Source: Bulbapedia and /dt on Pokemon Showdown.