Needle

[clavio]

Can you needle retrace? Whatabout flashback?

[ykpon]

Activated abilities always look like {cost : effect}.

[sunshine]

Both Flashback and Retrace are keyword abilities that let a player cast a card from their graveyard - they do not denote an activated ability. So, while you can name any card you want, you won't be able to stop a player from casting a card from their graveyard via retrace or flashback with Pithing Needle.