I'd imagine the reason you're having so much difficulty crafting a boosting sweeper is because Shandera simply isn't cut out to sweep whole teams. If I was going to go the boosting role (which I wouldn't because Scarf is better obviously) I'd just go Sub/CM/two attacks. Come in on something, boost up, kill it, kill whatever the opponent sacrifices to get rid of Shandera's Sub and then simply switch out of whatever they bring in for the revenge kill. Shandera has just killed two Pokemon and is still on 100% health...sounds awesome to me.
You're so caught up in creating some kind of unstoppable, 6-0 sweeper that you'll probably end up with something that's neither here nor there.
Uhhh,I don't really want an unstoppable force like that ._.
I just want to be able to sweep with as little support as possible.
Everyone knows Shandera can't sweep entire teams without crap like Aianto + Shandy or a mon locked into a fighting move >.>
It really isn't. Tentacruel doesn't possess the ability to do anything back outside of poison after one or two calm minds. Additionally, there's azumarril, you will always revenge you (90% minimum with aqua jet), but meh.
Tentacruel can do quite a bit of damage though:
196 Atk vs 215 Def & 261 HP (80 Base Power): 158 - 188 (60.54% - 72.03%)
That's with NO invesment in SpA. Though,even Modest 252 Sp.Attack Tentacruel can't always OHKO Shandy.
And I forgot how common Azumarill is./sarcasm