I like the simplicity of the wording here, but there's a subtle problem now that the rules say Scheme, Plane and Vanguard are card types. How much damage does a Tarmoblast do with this activated?

Tarmoblast

 

 U 

Instant

Tarmoblast deals damage to target creature equal to the number of card types among cards in all graveyards. (The card types are artifact, creature, enchantment, instant, land, planeswalker, sorcery and tribal.)

Because of the above comment, how about: The questions that the original stating raises for me do not concern Scheme, Plane, or Vanguard, but rather World Enchantment, Legendary {Land, Artifact, Creature, etc.}, and Tribal {Instant, sorcery, enchantment}. Also, it seems odd to make it a planeswalker, but that's just me.

Why does Tarmoblast count tribals but not legends or snow?

Because "Legendary" and "Snow" aren't types but Supertypes (like "Basic"). Oddly enough, Tribal isn't - I think because it needs to take a Subtype - although most people think it should be.