pro
great harass with e
free ignite with e
they don't expect magic dmg
con
harder to farm less ad
people think you are trolling

ok why play trist starting out ap instead of ad because with the ap start you can harass with e and stay at a far enough distance to make them back or die remember with ap your e and w get a boost so when they are low you can wer or just we when they die you can w your way out it helps your early game so you can become the late game beast that ad trist is known for