What word best substitutes for the difficult in sentence Harry is good at solving puzzles?

Here are a few words that could substitute for "difficult" in the sentence "Harry is good at solving puzzles," depending on the nuance you want to convey:

* Challenging: This implies the puzzles are complex and require thought and effort.

* Intricate: This emphasizes the puzzles' complexity and the need for careful analysis.

* Complex: This focuses on the puzzles' many parts and elements.

* Tough: This suggests the puzzles are hard to solve but not impossible.

* Tricky: This implies the puzzles involve cleverness and the need to think outside the box.

The best word depends on the specific type of puzzles Harry solves and the desired emphasis.