Found 'Spooky Trails: World 3-4' surprising easy. I made a few miscalculations which didn't really affect the battle, and reached the area in 7 turns. Not sure why I struggled so much years back; looking at my save file I used (Mario | Rabbid Mario | Peach) so obviously not making use of vampire damage. I didn't bother trying to fight the smashers since I could outrun them anyway, and used peach's extra jumping range to cross the gaps between the level.

The following levels after that were quite easy as well. I did need to retry a couple of times on the 'Calavera' midboss because of poor hindsight and positioning (anytime someone died I would reset). Got lucky with the burn effect from Peach which let Mario take two shots with 'Hero Sight', and allowed me to finish him off in the next round.

3-6 introduces the 'Valkyrie' enemies and I just love their BIG machine guns. Experienced some bizarre flickering while picking objects that infected Beep-O, causing the area around them to periodically glitch. Closing and restarting the game seemed to fix the issue.