The best class i would use to kill the horseless headless horsemann and MONOCULUS, would be scout. Usually his weapon's can be good, and he can run fast possibly avoiding most attacks.
Although what i would want improved in Team Fortress 2 would definatly be about hat restrictions. I mean, The good hats like the fallen angel are for halloween/full moon only. I would think there should be no restriction on any of these hats.
Also, GO MONOCULUS >

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When you fear to go to sleep, and you experience repeating nightmares, your experiencing Hypnophobia. When your Nightmares come to reality, your in deep shit.