Hardmode is a hard mode, as one can tell. Seriously. I've tried fighting The Destroyer with a Demon Scythe, Cursed Flames, Minishark, and my Savage Nights Edge. Full adamantite, too. Didn't work out too well. Tried fighting The Twins with exact same things. Still didn't work out. But I know have a Zealous Sharanga and a Nasty Shotgun, so I think I'm ready now. (We all know I'm not, though.)
My friend came over today. Tried the destroyer. Got close with my Shotgun, Minishark, and Clockwork Assault Rifle. Haven't tried many tips you guys have given me, except the grav potions and the arena. Grav potions barely helped, but that's because I'm bad. And for the arena, I built it too high. Again.