Welcome to this in-depth guide on how to dominate the Rift with Katarina, the Sinister Blade. As a high-mobility assassin, Katarina excels at quickly eliminating her foes and turning team fights in her favor. In this guide, we'll cover everything from itemization and ability usage to laning phase strategies and teamfight tactics.

Play safe pre-level 3, then use your Q and E combo to poke and trade efficiently.
Roam when possible, especially after reaching level 6.

Look for picks in the jungle or side lanes.
Prioritize objectives and help secure vision for your team.

Focus on assassinating key targets in team fights.
Use your mobility to split push and create pressure in multiple lanes.

Wait for the right moment to engage, and try to catch the enemy carries off-guard.
Use Zhonya's Hourglass during your ultimate to avoid getting burst down.
Clean up fights by repositioning with Shunpo and taking advantage of resets.

Practice animation cancels with your abilities to maximize burst.
Utilize ward hops with E (Shunpo) for unpredictable escapes or engages.
Keep track of enemy crowd control abilities before going all-in.

Katarina is a high-risk, high-reward champion that requires practice to master. Adapt your playstyle based on the game's flow, and always look for opportunities to snowball and carry your team to victory.
Remember, this guide is a starting point, and adapting to specific game situations is crucial for success with Katarina. Good luck on the Rift!