Since the Switch release added Character abilities with Grand Prix mode the devs were at least kind enough to let function work in the main game.
Pyramid Head (and also Arbiter from the latest update) have the ability to kill an enemy with their blade at the cost of speed. This works wonders in campaign. Press
as an enemy approaches to use your ability to just stab them with ease.
Continues are very costly on Expert and it's recommended you grind gems before attempting this difficulty. If you don't wish to pay for a continue you can always close the game and relaunch to not get sent back to the start of the World if you can't afford the continue. This won't bring back all your lives like a continue will but gives you a chance to progress a little further.
For reasons I'm not sure after paying for so many continues the game starts offering free continues. I believe this is because your star rating drops down to 1 star but we aren't trying to 3 star every world so this is more than a lucky break.
There is 6 world's in the game before you hit the credits. This version launched with the Switch's 7th world title update which is where the devs have set this achievement to be unlocked. So you must hit the second credits sequence before awarded the achievement.
Difficulty doesn't stack unfortunately. So unless you're experienced in Bomberman I'd work your way up to this.
Co-op is local only but you share lives with your friend so unless they are experienced I'd go it solo. If you do bring a friend having a tag team of Arby and Pyramid Head will help cut up all the enemies quickly.
Some characters like Alucard can dodge bomb blasts if you get the timing down but I feel our Melee characters are best suited for the job. Though they won't cut through boss fights.
Good luck and enjoy. This game isn't quite Saturn Bomberman good but their attempt at making another game similar to the SNES games turned out great imo and after all the title updates adding extra content I feel the game has just gotten way more meatier.