What's this? A Mario Maker thread? Why don't mind if I do.
My levels mainly showcase difficult boss fights because that's the thing I enjoy, and I enjoy playing them. The vast majority of my levels house difficult bosses. Here are most of the levels I've uploaded.
JCR-85P-5HG (organic boss) A boss fight against one organic boi.
WQF-L5L-LNG (spoopy boss) It's a fight against a spooky boi. I'd say this is one of the harder ones, so enter with caution.
J2X-60M-39G (bossly manor) You fight 4 mini-bosses in a manor, then you go on to fight a big boss.
K1S-3ML-VNF (basic boss) It's a basic level with a basic boss at the end. You've got nothing to worry about /s.
D6H-NR5-9KG (toxic boss) This boss will probably start trash talking you if you die too many times.
WJN-D2P-S8G (Wiggler's temple) A desert temple full of wigglers.
RXH-V0M-J5G (Mount Majesty 1)
YKV-W2P-W0G (Mount Majesty 2)
P3Y-4DR-CYF (Mount Majesty 3) This is a three part series I made based on a mountain that's soon to erupt, and it's your job to stop it.
DGW-DKH-00G (Poisonous Peaks) There's poison everywhere
9TF-0V3-QLF (Difficult Boss) The first of the difficult bosses that I made and probably a good starting point to get into the rest.
713-34H-G7G (Morton) A Morton boss fight
H1G-K0F-7JF (Ludwig) and a Ludwig boss fight (one of the more fun fights IMO) Edit: I just re-uploaded this one not too long ago, and I buffed its difficulty in the process (details of the buff are in the comments)
5LG-G3F-NXG (Mechanical Boss) A boss fight with a good amount of TECHnique to it (not sorry)
Y0K-YNN-5NF (King Skele) This was made as a final boss for my super world, meant to be unfair and insanely difficult.