"Toho medvěda potřebuju pro ni."

Translation: I need that bear for her.

[TTDan]

I would have thought that 'Toho medvěda potřebuji pro ní' would be more formal. Why the choice of potřebuju?

[Jamie08MD]

Both potřebuji and potřebuju are grammatically correct. Like you said, "potřebuji" is used in formal texts, "potřebuju" is used pretty much everywhere else. You've made a little mistake there though. You need the accusative "pro ni" (short i).

[pdusek]

Confirming. The difference between "ni" (short) and ní (long) can be very important. Try to think of a sentence "Myslím na ni. Making the same mistake (na ní) will change the meaning from "I think of her" to "I think on her." Very easy way to get slapped ;-)