This is admittedly a weird one with very little, if any, mechanical synergy. The bloodblade class mostly wants Constitution and Intelligence and the druid class wants Wisdom and largely doesn’t care about physical ability scores due to wild shape. In addition, both classes have very different focuses in terms of how they play. Bloodblades are primarily a martial class and druids are a spellcasting one. Both also have a number of key class features. This combination is probably best for advanced players with a clear vision for what they’d like to do. Flavor-wise, there’s a bit more to work with; the idea of a druid infusing themself with supernatural blood is kind of a fun concept to work with, and there’s definitely ideas to work with for a “blood druid.” Focusing on bloodblade levels will give you a dangerous martial character with a bit of nature magic and some shapeshifting that’s useful in non-combat situations such as traversal and spying. Focusing on druid levels gives you a powerful, shapeshifting spellcaster that has some inherent powers from their magical blood that they keep access to while wild shaped. An even mix of the two will probably be rare, but represents a highly-unusual fighting spellcaster. [[Synergy Feats for Multiclassers#Bloodblade w/ Druid|Bloodblade-Druid chains and ideas]]