Hard Mixed Cocktails

Long Island Iced Tea: Contains multiple liquors like vodka, rum, gin, and tequila, along with cola and citrus.
Three Wise Men: A strong mix of three whiskeys.
Sun Crush: Another strong, short cocktail that can be made with whiskey.
Chicago: A classic, strong short drink.
Cardinale: A classic, strong short drink made with gin. 
Ramos Gin Fizz: Requires a vigorous shake to create a thick, frothy foam.
Vieux Carré: A historic and delicate drink that requires precise balancing of multiple strong spirits, like rye whiskey, cognac, and sweet vermouth.
Bloody Mary: Considered one of the most complicated drinks to make from scratch because making it well from scratch can be a feat.
Sazerac: A classic cocktail that can be tricky to get right, involving absinthe and a balance of other ingredients.
Martini: The "hardest to master" for some, due to the delicate balance of spirit and vermouth, notes VinePair.
Mai Tai: A tiki cocktail that is a "positively transcendent experience" when perfectly executed.