When I was leveling up in this game I used to main ap tristana. Back then she had 0.8 ratio on w, 1.0 on e, and 1.5 on ulti and had 60 second cooldown. I used to one shot the enemy mid laner every 60 seconds if they don't buy mr. Then I would roam bot and 1 shot the enemy adc.
JJI7441 votesConsider E and R are point and click, ranged and unavoidable.
Now realize you answered your own question.
Dark Nephthys1 votesAP 
still works, it just requires a different play style and has a little bit more counter to it. I used to play AP Tristana a lot back in Season 3 or 4 I don't really remember and I'll occasionally play it in this season as well.
Back then you would just rush death fire grasp, and then jump on the target to damage + slow, then deathfire + E + Ignite + 1-2 Autos + ult and that would basically 1 shot anyone (some times you don't even need the 1-2 autos) and they will just burn out from the DoT from her E and ignite. The problem back then was that after that, you would just kind of sit around auto attacking for weakish damage, waiting for death fire + E to come back in a team fight. It was great as a 1 person instant kill that would basically make it a 5v4 from the start.
How it is now is you would get Nashor's Tooth as your first item. Jump towards the target and in mid air throw your bomb on them, land on them, Ignite + 2-3 Auto attacks + Ultimate and with Thunderlords, they would generally die. Then get the reset on your jump (even if the target didnt die, you'd get the reset on your jump) and can re-jump on another target using nashor's empowered auto until your E is back.
Overall, the damage of AP Tristana only really drops due to the removal of Deathfire grasp. As for her other abilities, yes her W does less damage but gets resets on full stack bombs and from kill/assists so she can reliably use it more often in a team fight. Her E technically does more damage (at least AP ratio wise) since her E can deal 110% AP when maxed and fully stacked, it's just got more counter play to it since the target can walk away to avoid you stacking it or Zhonyas or other abilities to avoid the explosion. Also since CDR is so rampant now in AP items, it's much easier to get max CDR to have your E and Ult off CD more often. The AP ratio drop on her ultimate did hurt her in AP but to be fair, 150% AP Ratio on that ult was a tad bit OP. Plus now you can use your E for help taking towers, even with AP those bombs + auto attacks can still do great against towers.
tldr: She can be played as AP, and she doesn't do that much weaker then she used to but has more counter play. You just got to get used to her new play style and get used to throwing in auto attacks in her combo, which her old AP self didn't need.
