Blockland would be rated M (17+) or 16+ (Pegi.)
Since the "Speed Kart" update, blood and gore were added default.
Blood and gore fall under a "Mature" rating.
BUT
Before the "Speed Kart" update, this game would have been at least rated T (Teen) or E 10+ (Ten and older) because of it's violence, but "Online Interactions" I believe would fall under a "Teen" rating.
But, "Online Interactions" would not affect the rating as far as I know.
But again, as of now in my opinion, Blockland because of it's gore would be rated M.
Again, "Online Interactions" would not affect the rating, so if a server has research n' stuff, that would fall under "Online Interactions." But the creator would have to warn the players (you) or the parents of it's content via e-mail or via text (website etc.)
All I know, and I did not look up any information, I just thought of this in my head.