Hello Crushie and welcome to TASVideos.
There are multiple visible issues that exist in this TAS. But before we do go through that, I'll mention the elephant in the room for you. In DKClassics the ladder glitch does not exist.
However, because of that we can compare that on a surface level to a previous TAS
made by Phil back in 2005 which was done on Game B and doesn't contain the ladder glitch.
A more modern, comparison to DKClassics which removes the surface level comparison
is this movie file I made which is faster by 490 frames.
By no means what I made is perfect either. It has issues at Elevator section but it showcases what should be done, which is also outlined in other previous TASes.
When crossing past ladders that you aren't climbing, a quick Up, Down saves several frames (Down, Up for when they're below you).
This TAS also started out as an "all items" one before neglecting an item of Pauline's and in fairness
the Original Edition TAS fills out that quota.
Please take your time and use the tools available to you in FCEUX and
use the userfiles.
Go again when you've optimized all you can.
