Ball's gaining isn't conditional on taking the -$1 token, so you can buy multiple Balls on the same turn without taking the -$1 token after the first purchase of the event.
Oh, yeah. I forgot about this (even though I used it recently). When Ball is good, a double Ball with 10 coins and an extra buy is really good. I think I picked up four Advisors with this in a recent game to win the split.
This reminds me of something I was thinking about recently:
0 Advisors: Good for your deck
1-2 Advisors: Bad for your deck
4+ Advisors: Draw your deck
Only somewhat.
Advisers are a trade off between how likely are you to see power cards this shuffle vs how fast do you shuffle them back in and any new cards.
Say I have Swindler/Adv as my opening. The odds that I will see my Swindler get discarded off Adv are 3/11. On the flip side, my shuffles go from 2.4 turns down 1.8. Oddly enough the expected number of times I hit my Swindler is going to be ~.4 in
both cases (no Adv is about .01 better). Adding in a second Adv increases the odds of my Swindler getting tossed to 5/11, but now my shuffles are around 1.4 hands each. This only drops me down to around .39 Swindlers/hand.
However, as I add more good cards or junk the starting cards I decrease the number of complete whiffs (from Adv hitting 2 good cards) while still shuffling faster. The lower the variance in card value, the better Adv gets. Just buying Silvers will tamp down the the hurt of discarding your best card.
We know 2 Adv cannot be straight bad for your deck ... otherwise we would literally discard coppers over Adv. Sure the is an opportunity cost to having the Adv, but there is also one for Silver.
Similarly 4 Adv alone is normally not quite sufficient to draw deck. You start with 10 cards, each Adv draws draws +1 net (replace the Adv, discard best card, draw +1 card), each hand starts with 5. With a starting hand of 4 Adv, you then will hit 9 cards ... but odds are at least one Adv will be buried so deck drawing waits until you have 5 or 6 ... or some other draw (even things like Cellar and Warehouse).
In general, I have found Ball to be pretty solid if I want to spam stuff at $4, at least once I have gotten my expensive $5s or higher. The $10 double buy is massively worth it often.