I got a question for you: Super Smash Bros. was introduced in 1999 for the Nintendo 64. It was released worldwide after selling over a million copies in Japan. It featured eight characters from the start (Mario, Donkey Kong, Link, Samus, Yoshi, Kirby, Fox, and Pikachu), with four unlockable characters (Luigi, Captain Falcon, Ness, and Jigglypuff), all of them created by Nintendo or one of its second-party developers.

Based on this passage, how many unlockable characters in super smash bros?
Let's think first:
To answer this question, we should know that: It featured eight characters from the start (Mario, Donkey Kong, Link, Samus, Yoshi, Kirby, Fox, and Pikachu), with four unlockable characters (Luigi, Captain Falcon, Ness, and Jigglypuff), all of them created by Nintendo or one of its second-party developers.
Therefore, the answer is four.