Dialects:
Regional American -- especially Southern, New York, New England, Mid-west, "Valley";
British - Standard, "Cockney," some regionalisms like Yorkshire, Irish, Scottish;
Australian, Canadian;
A quick study in any English Dialect
Accents:
French, Italian, Latino, German, Asian;
A quick study in mimicking any foreign accent in English.
Impressions:
Christopher Lloyd, Rod Serling, Kermit the Frog, Rowlf the Dog, Grover, Yoda, Dudley Moore, Sean Connery, Humphrey Bogart, Edward G. Robinson, John Wayne, Marlon Brando, Willie Nelson, Johnny Carson, Homer Simpson, Marge Simpson, Moe, Apu, Mr. Burns, Mickey Mouse, Joan Rivers, Patricia Neal, Ed Wynn, Brad Garret, Winnie the Pooh, Bullwinkle Moose, Bill Clinton, Julia Child, John Houseman, Daffy Duck, Elmer Fudd, Many many many many more!
Characters: Anyone, anywhere, at any age, in any time.