Learn Russian: Неужели наш шпион слишком хитёр, чтобы провалить эту миссию? - Is our spy really too cunning to fail this mission?

Russian pairs слишком (too) with чтобы (in order to). Literally, this sentence translates to "too cunning in order to fail." You will use this слишком ... чтобы + infinitive pattern whenever a quality is so extreme that it causes a specific result—or in this case, prevents an action from happening.

What nuance does неужели add compared to a standard yes/no question?

Неужели expresses strong doubt, surprise, or disbelief. While a regular question just asks for a fact, starting with неужели translates closer to "Is it really possible that..." or "Can it really be that..." It shows the speaker finds the idea of the spy being this cunning almost hard to believe.

Why is хитёр used here instead of the standard adjective хитрый?

Хитёр is the short form of хитрый. In Russian, short-form adjectives are strongly preferred when the adjective acts as the main predicate (the core "is [adjective]" part of the sentence) rather than just describing a noun. Using the short form here makes the statement sound more definitive and slightly more literary.

Could I use a different verb for "fail" here, like ошибаться?