In Ramayana, Hanuman killed hundreds of Rakshasas after he has found Sita in Lanka.
Some interpretations say that the army he took with him to Lanka consisted entirely of avatars of a single deity. (This is hard to pin down, and no deity seems to have that many avatars, but there are many deities and many interpretations of each one in Hindu practice.)
The early Welsh legends about "King" Arthur (found in, among others, Historia Brittonum) claim that Arthur personally killed more than 900 Saxons in the Battle of Badon Hill:
"(..) there fell in one day 960 men from one charge by Arthur; and no one struck them down except Arthur himself." (Section 56)
"In this engagement, nine hundred and fortynote Yes, the book is at odds with itself. fell by his hand alone, no one but the Lord affording him assistance." (Section 56a)
In the Táin Bó Cúailnge, Queen Medb decides to invade Ulster just as all of its men fall ill due to an age-old curse. The only soldier unaffected is the teenage Cu Chulainn. He manages to single-handedly hold off Medb's forces for months - and this is before he goes into a warp spasm.
Huitzilopochtli (as befits a war god, of course). The first thing he did upon being born (fully grown) was kill 400 gods.
And of course, we can't not mention biblical Samson, known for slaughtering one-third of a three thousand-strong army before the rest fled, with a jawbone.
Samson's got nothing on Jesus, though. The Book of Revelation says that when Jesus returns, He's going to one-shot an entire army.