When using Slowpoke's "Rambunctious Party" attack, can I choose no Basic Pokemon even if some are in the top 5 cards I drew?
Yes, you can choose as many or as few (including zero) as you like.
Source: Undaunted FAQ (2010-09-09), PUI Rules Team (2010-09-09)

Relevant cards

Note: All applicable cards may not be listed below.
HGSS3_66