It all comes down to the Scarab Hive rule in their entry:
Nominate a Canoptek Scarab unit within 6" and roll a D6. On a roll of 2-6, add one base to the Canoptek Scarab unit - the base can move an act normally this turn.There is however no limit, currently, for where to place that new base, observe:
|Start of turn, you have your Scarab swarm and three units of Spyders.|
|Place your first three bases.|
|Now the next three.|
|And the final set.|
|6" Move forward|
|...and Assault 12".|
Some quick math shows 8 bases crossing the deployment zone, with five attacks each that auto hit and with half having the Entropic effect, you will have 20 reduced armour points right there. With the amount of your move, you have plenty of opportunity to multi-charge a number of units, all for the low cost of 495 points. Oh, and you have the rest of their army to contend with.
Now before you get up in arms about this, there is an important thing to keep in mind: this is not a player's fault. You may have an opinion on this, but someone else from a different background could have a completely different view. A player who plays lots of Warmachine, for example, would see this as purposeful design. Is it? We won't know until that FAQ comes out about six months from now.
Like any editorial, this needs to end with a 'call to arms': the solution is not to hassle people pointing this out, but to find a way to get in touch with the editors at GW and let them know that things like this are not okay, that rules have to come out clean and that a six month lag between release and FAQ is not acceptable... Unless this was done on purpose, in which case I will just shut up.