I'm not good enough to execute it in a single segment, but I think the fastest way to get 2-Castle 100% is as follows.
Start as mini, go through the door to outside at 72 Switch to Fire Mario right before the boss fight, finish at 31 (1:09 run). I'll try to get it single segment or at least close to that on video unless someone is able to get it before me.
The Tool-Assisted Speedrun gets a 436 starting as fire mario:
Staring as mini mario would probably be a timesave since you don't need to spend time collecting the powerup.
By the way, anyone who hasn't watched this TAS yet absolutely should; it's amazing.
Earlier today, Twitch has that they are "implementing a 100 hour storage limit for Highlights & Uploads starting 4/19." There is a 2 month grace period for people with highlights on their channel to be able to download their highlig
