Lag affects the game experience drastically (timing for dodge is completely unpredictable), allow changes in quality, there is no reason not to and is a simple fix.
AP points are pretty useless when improvements do as much as 0.02% difference to a stat, the concept of levels exist for character development, either make it matter or remove it.
You should have mentioned that we MUST start on easy (the fourth boss was insane on medium and a weakling on easy) or balance those difficulties.
The game over screen is unresponsive before the shift completes.
Only bosses, no enemies whatsoever, but considering the lag that is a blessing. Maybe you've got some nested loops running? Last time I checked flash wasn't supposed to get this slow.
If you did that by yourself, it's an amazing game! The combat is based on old classics and the bosses attack patterns differ enough. Sad the only 2 bosses you can combo are the first and the last, and if you're really fast (and your computer too) the cave demon. Ground mobility is OK but air mobility is welcome and could help add depth to the fights, allowing another way to dodge low attacks and attack high enemies.