Arrowed
Been loving this Thread so I thought I'd respond with one of my own.
My personal favorite Smackdown.
Requirements: PHB
any spellcaster with Telekinesis.
1 Wagon of 10' cubed dimensions. (Pretty average for a wagon really)
Now, all you need to do is fill the wagon with arrows.
The telekinesis spell description states that a caster can throw multiple objects weighing up to 25lbs/caster level. At the minimum caster level this allows a wizard to violently thrust 1500 arrows at their opponents. (3lbs for 20 arrows according to the PHB)
Now since they deal weapon damage let's use shortbow damage of 1d6 that amounts to an earth shattering 1500-9000 damage in a single round. And due to a natural roll of 20 automatically hitting, that results in 75-450 damage regardless of AC.
and all of this done by a lvl 9 character.
The only way around this is damage reduction, but it still remains the best anti giant/army tool I've seen yet.
<edit> To bypass damage reduction simply light them all on fire first and deal 1500 fire damage instead
You could always invest a lot of time and money into making 112 daggers +5 for an attack that deals 672- 1008 damage against pretty well anything.
Enjoy!