How many Scarabs does it take to destroy a vehicle?

Less than 42, for sure :)

So, in the chart above, 'destroyed' includes both the wrecked and explodes! results. The vehicle is assumed to be stationary, thus hit automatically; I'll be getting to do run the numbers on moving vehicles a bit later, same with stunned, immobilised etc.

AV 10 will be most vehicles, as most have rear AV 10; some Leman Russes and other Necrons will be showing off AV 11, Monoliths and Land Raiders naturally have AV 14 all around. I can't think of anything with rear AV 12 or 13 at the moment, and dreads using their front armour won't be hit automatically, voiding the results above... but I've included them for completeness. Never know what crazy stuff will be in the next codex hey ;)

You can see that a mere 3 charging scarabs is enough to wreck most stationary vehicles in the game (95.56% and 88.62% respectively)! Entropic Strike really is that good, at least while applying the AV reduction before the roll to penetrate! At least that's how I read it, we'll see if the FAQ tones things down a bit... even AV14 vehicles can be comfortably handled by 5 charging scarabs (95.54% chance of destroying it), although using only 3 is a bit more touch-and-go, but still within the realms of possibility (43.56%).

For comparison, a BS4 melta-gun has a 32.41% chance of destroying an AV 10 vehicle. A squad of four such guns has a 79.13% chance of destroying an AV 10 vehicle.

Pretty good, eh?

It's clear, armour is no defence against scarab swarms. How useful going faster (or hell, moving at all) will be in protecting yourself, we'll examine next installment.