Place rocks ice into a rocks glass
Pour 0.1 oz of ginger syrup, 0.1 oz of agave syrup, 0.1 oz of maraschino syrup, and 0.5 oz of mezcal into a mixing glass
Add 2 dashes of Peychaud's bitters, 4 dashes of Angostura bitters, and 1.5 oz of Highland single-malt whisky
Fill the glass with ice cubes and mix with a bar spoon
Strain into the rocks glass
Garnish with grapefruit zest