In many ways, the Spellbook is a better recovery option than Locations because Ruby/Amethyst has not answer for it, while it can pretty reliably take out locations via Maui
Brawl Legal Vintage Legal Timeless Legal Commander Legal Pauper Not Legal Oathbreaker Legal Penny Legal Toolbox Buy This Card Notes and Rules Information for Lathliss, Dragon Queen: If Lathliss enters at the same time as one or more other nontoken Dragons you control, its second ability will trigger once for each of those other Dragons
The Breed Lethality deck is particularly good since it introduces the Phyrexian Angel Atraxa, with her original card, Atraxa, Praetors Voice
This card could even see play today if reprinted into Standard format, with VMAX Pokemon running around
By itself, it offers a pretty fast clock thats very difficult to stop, which to me makes it an ideal threat in a deck like Delver that just wants to apply a bit of pressure while keeping the opponent off their game