Chillax in singleplayer followed by
Okuplok saveless
Then new sunder maps
also Vhard.wad is another really hard one
speed17 has some really bullshit fights
I also made a fairly hard map for the speedmapping competition which I think might interest you if you like hard maps
Not the hardest but the gameplay is really ridiculous kind of like the maelstrom finale but with more ammo and health lol