Each alternate class feature presented in an archetype either replaces or alters one or more specific class features from the base class.
When an archetype includes multiple alternate class features, a character must take all of them—often blocking the character from ever gaining certain standard class features, but replacing them with other options. All class features of the base class that aren’t mentioned among the alternate class features of an archetype remain unchanged and are acquired normally when a character reaches the appropriate level. If an alternate class feature replaces a base class feature, the archetype doesn’t count as having that base class feature for the purpose of meeting any requirements or prerequisites. On the other hand, if an alternate class feature alters an existing class feature, it is considered to be the core class feature for the purposes of meeting any requirements or prerequisites, even if it was renamed.
A character can take more than one archetype, but none of the alternate class features can replace or alter the same class feature of the base class.
If a class feature has a series of improvements (such as a Fighter’s weapon training or a ranger’s favored enemy), it can be replaced either entirely or partially. By default, an alternate class feature replaces the entire original class feature and all of its improvements. For example, if a class feature states that it replaces trap sense without mentioning a specific bonus, it replaces trap sense entirely.
If an alternate class feature replaces one instance of a class feature that’s part of a series, the next time the character would gain an improvement to that ability, the new improvement counts as the lower-level ability that was replaced by the archetype, and all subsequent improvements follow suit. For example, if the barbarian’s 3rd-level trap sense +1 were replaced, the barbarian would gain trap sense +1 at 6th level, trap sense +2 at 9th level, and so on.