Your goal is to win toplane, but Assasshen can still be played against matchups that are very difficult due to Shen's powerful toolkit. In a case of a difficult matchup, you need to keep tabs on the enemy jungler, as you can literally kill just about any single jungler in their own jungle when they're doing camps or trying to do Herald. Keep vision on these areas and leave the lane if possible to take your extra gold.

Your taunt should be a death sentence against quite literally 90% of junglers even relatively early.

On lane Shenchanter shines as a counter-engage champ. He makes all-in an almost impossible aspect as he can dictate the fight through his taunt. By taunting the ADC you can shift the engage onto its head, as the enemy engage support likely has burned the entire kit on your ADC.

Against more vulnerable lanes, such as Lux, you should be taking Glacial Augment, and look for the engage yourself. On an engage on Lux or similar squishy support, you are at the minimum burning the Lux's flash. Morgana is the only one you should be wary about engaging this way.

Later as teamfights start, Shenchanter should keep position in middle of the fight preventing enemies from engaging on the carries and disabling their carries, depending on the situation. You should not be the first one in, but your taunt should always make a significant difference.