Tips/Cheese on the 2nd Floor Museum Boss fight:
The enemy Hypno has 2 attack move: Drain Punch (Fight type/10 PP) and Psybeam (Psychic/20pp)
It also has a passive where it Sleep your first pokemon and recover HP/Status once defeat the first time
There is a way you can beat it with just 3 under pokemon:
Capture a Ghost type pokemon there is one on the West of the first proper town, a (Ground/Ghost)
-1st pokemon will be your unfortunate bait for the sleep, let it get defeated
-Next, toss out your Dark type starter
--This turn, the Hypno will definitely try to Drain punch, which likely one shot your mon. Here, you must immediately swap to a ghost type Pokémon
--The Drain Punch will be immune due to Ghost typing.
-Now, it will want to do a psybeam, sadly, our Ghost type Pokemon is a bit ... weak. It likely will not survive this. So, switch back to your Dark type starter.
--Oh? What this? Now the Psybeam will be negated by the Dark type?
---But it will try to Drain Punch you... which you must swap to your Ghost type...
-----You can see where this going
-Repeat this until the Hypno does not try to Drain Punch after you swap out anymore (20 swaps)
--Wreck it with your Dark Type Pokemon
----Grofit
I played on slightly elevated difficulty, so you might brute force this on easier difficulty.
Thank you for coming to my Ted Talk
My team after the fight, no item used.