Prepare Chocolate Skulls: Melt dark chocolate in a microwave-safe bowl or over a double boiler, then pour it into skull molds. Refrigerate until set, about 30 minutes.

Make Vegan Buttermilk: In a small bowl, combine soy milk and apple cider vinegar. Let it sit for about 10 minutes to curdle.

Combine Wet Ingredients: In a large mixing bowl, stir together the curdled soy milk, instant coffee granules, apple puree, olive oil, and vanilla extract until well blended.

Mix Dry Ingredients: In a separate bowl, whisk together flour, cocoa powder, baking soda, sea salt, caster sugar, and muscovado sugar until evenly combined.

Combine Mixes: Gently pour the wet mixture into the dry ingredients and whisk until just combined; avoid over-mixing.

Bake: Distribute batter into cupcake liners, filling each about two-thirds full. Bake at 180°C (356°F) for 22-25 minutes or until a toothpick inserted comes out clean.

Make Coulis Filling: In a saucepan, simmer blackberries, sugar, and water over medium heat for about 12 minutes. Cool and refrigerate once thickened.

Core Cupcakes: Once cooled, use a cupcake corer to cut out centers and fill with cooled blackberry coulis.

Prepare Frosting: Divide vegan buttercream; mix half with leftover coulis and the other half with cocoa powder.

Decorate: Pipe frostings onto each cupcake, top with chocolate skulls and fresh blackberries.