Just gonna post the missions I've completed and the times on them. With any luck I'll be forced to update this often as I complete the missions (if I dont, I'm a noob at one of them and cant beat it no matter how hard I try )

Mission 2 Widow Missileer 1:06
Mission 3 Wastelings 11:29
Mission 4 Vincent the mage 13:29
Mission 5 Deep Labyrinth 16:39
Mission 6 Boxemon 1:32
Mission 7 Gatling in the Wastes 3:15
Mission 8 Lord of the Jungle 20:39
Mission 9 Cait vs the world 9:44
Mission 10 Missilebreaker Melee N/A
Mission 11 Collectors Mind 4:37
Mission 12 Vincent the destroyer 8:21
Mission 13 Rains of Gehenna 28:08
Mission 14 Vincent the Grappler 6:59
Mission 15 Red and blue 1:43
Mission 16 Stygian Sewers 6:07
Mission 17 Messenger from Hell 1:38
Mission 18 Badlands 12:44
Mission 19 Chamber of Ghosts 8:28
Mission 20 Deep Tower 11:53
Mission 21 Cait vs the crimson 2:02
Mission 22 Shinra Manor Prime 2:33
Mission 23 Rampart Rumble 4:31
Mission 24 Contra Kalm 14:42
Mission 25 Missilebreaker Deathmatch (havent done)
Mission 26 Cait vs the Cerulean 2:49
Mission 27 Vincent the Beast N/A
Mission 28 Cyclopean Causeway 2:29
Mission 29 Trick Arc 5:42
Mission 30 100,000 Needles 10:07

Me stucks on the dual horn 1 lolz it does my nut in

You just gotta keep running around and get shots off at him once in a while, the key is to make sure you're safe before you start shooting. If you think you might get hit by taking a shot at the horn then dont try it, just keep running. If you find you run too slow you can either switch to a weapon that's light while you run and then quickly switch to a heavier one to shoot or just put a good gravity floater on your big gun.