Another time to consider Island is when you have otherwise built an engine, but end up with a spare $4 during the build-up. For instance, on a colony board you may hit $7 and your best option is to grab Island/Silver so that next turn you can mat your trasher and then buy Plat (this assumes that the $1 differential between Gold & Silver is not worth a card). This is risky if you don't currently have overdraw, but netting 2 VP and a slightly more reliable engine when you do have overdraw in a deck drawing engine can go a long way.
I think I covered this with the sentence: "If you have a nice engine in a slim deck that's afraid of green cards, you can consider it to exile your Provinces, but make sure that the late thinning is really necessary." This is the rare case of when Island is okay because it just fits into the current turn perfectly, even if there is no enabler. Or do you think that's something different?
There are two things that make this slightly different, one is that this is a buy for a single card, normally your trasher, so it can be applicable before you get to greening. (e.g. if I'm going to build up to $22 it can make sense to spend the $4 when I'm at $7 or some other price point long before you get green) and secondly it can become more important if your trasher is some sort of stop card in your engine - e.g. a mandatory trasher in a Wt draw engine so it reduces all subsequent Wt draws by 1 card, if you need to use Golem or Herald as a village, or if you are using cards like Farming Village, Wandering minstral, or Journeyman where one card type greatly decreases your ability to flip past junk. On the high end, having something like Trading post/Golem makes Island on the trasher obscenely powerful, on the weaker end it is just grabbing something to get rid of a dead card (like province), somewhere in the middle is setting up one huge turn and nixing a dead card for more reliable draw. For engines, the payout for Islanding one card can vary a lot, as can the opportunity cost - even when it isn't worth Islanding provinces it can be worth it to nix the trasher.
I don't consider Gardens an enabler for Island, I think it's a trap. A Garden deck is usually huge, which makes the thinning from Island almost irrelevant.
That depends on if Gardens are contested or not. If they aren't, then Island is very nice. It takes only 8 gains to empty the pile which is often 1.5 turns shorter than piling out a kingdom card and they are worth double the points of Estates. If your opponent goes something Garden intolerant, then you can hide your estates and get by with fewer early enablers; further most Gardens enablers work pretty well with Island.
Silk Road can certainly be a reason to buy it, but almost exclusively for the VP rather than the exiling. You very likely shouldn't buy Island it over Province or Silk Road, so if anything you'd buy it over a Duchy, which I don't think is important enough to deserve a mention.
If Silk road is not going to be contested, then you should go Island early and keep a steady mix. Exiling the estates and the odd Silk Road does increase the frequency with which you hit enablers. If some of your enablers are non-terminal (Iw being king, but also things like Candlestick maker and Pawn) it really does increase the rate at which you pile down green.
In both the Gardens and Silk road cases, the question is can you risk gaining Island instead of Gardens/Sr, but honestly that is the risk with virtually
all Gardens/Sr enablers except maybe Iw. In a mirror, you have to be very careful and often lucky to not overbuy enablers and come up short on the Garden/Sr split.
I agree that all of these can be theoretical reasons to buy Island, but I honestly don't think any of these cases is relevant enough to deserve a mention; I consider them edge cases.
More I'd go with Alt-VP being a mention; Island does work really well when you are bloating out a Vineyards deck as it counts twice and can hide your Vineyards. For the rest it applies mostly on boards where things are non-trivially obvious.
I don't think Pool enables Island. I agree that trashing is good for SP decks, but Island is just a really slow trasher, every other trasher is probably better. And yeah, Island is an Action card and can be drawn with SP, but so can any other trasher.
Yeah, but only Nv can sock away green to keep your pool deck reliable as it scores points, and on a lot of Island/Pool boards there will either be no other trashing or stuff that isn't so nice at trashing - like Hermit or Counterfeit that makes Island good at popping off stop cards that would otherwise be left.
I don't think I ever had a game where using Transmute to trash a card with several types was strong.
It is a pretty good thing when the deck already supports Transmute for some other reason. For instance I did a Pool/Transmute/Familiar/Necropolis/Remodel/Island deck. Potion was a given with both Pool and Familiar, Transmute was decent at killing Curses and coppers and then tossing in Islands let me get golds to remodel to Provinces without having to spend multiple turns going Transmute -> Duchy -> Gold -> Remodel. Again this is only good if you've already gotten Transmute for some reason that negates the opportunity cost (e.g. you hit $1P on a Familiar board) and you can use a lot of card value or reliable draw to pair up Island & Transmute.
Again, I don't see this as relevant enough to be mentioned. If it was Great Hall, sure, but Island sets itself aside after you use it once, so you're not likely to hit it with Ironmonger more than once.
Most likely not, but the point is that Island is a bit better during the buildup if you are doing Ironmonger, I'd take at least a few if I have a low opportunity cost way to get Islands.
Well, I have only been able to use a 3 pile of rats to end the game like once or twice in my career, although I often hoped for it, and I don't think Island is a crucial part for that. You can also do with fortress and VP's in your hand, with a victory chip, with a curse in your opponents deck, or just by buying an Estate at the end of your turn with virtual coin.
Absolutely correct, on the other hand Island is one of the easier ways to keep the threat an option after the opponent gets a province. Again I say this more because it is really fun to do rather than it being really strong thing.
using Island to protect your Provinces as being a thing, but it would require both swindler (as it is the only card which can kill a Province effectively), Prince or Peddler, and decent enough support to make it better than a silver. That's too narrow.
You are forgetting about Alt-VP. Fairgrounds, Silk Roads, and sometimes even Feodum and Gardens all can be killed by Knights, Rogue, Swindler, and Sab (if Sab can be played enough).
I highly doubt that using Island to prevent your opponent from abusing the synergies with Possession works. For one, Island is one of the three main synergies (as you said), but also because both of the other two (Amb and Masq) can hand out cards to your opponent; so even if you go through the trouble of exiling your masquerade with Island before he can play Possession, he can just pass you another Masquerade with little effort.
More aptly, he can pass you a Masq or Amb
one turn later than if you have the Masq or Amb already in deck for him, which can be long enough to win the game. Spend $4
late game for an extra turn? That is a pretty good trade. Further, if your opponent cannot play both Possession and Masq/Amb the same turn (e.g. a no-village engine), then you can keep setting aside the poison card they give you.
The general case is also of note. You should at least highlight the dangers of Island in Possessed decks (e.g. attack cards can be lost) but on the other hand if you want to kill your deck so it cannot purchase provinces (instead it just Possesses the other guy and maybe buys more Possessions), then Island can be a decent way to get under $8. For example If we are playing with a Kc/Possession dominant setup (say something like Journeyman/Wandering Minstrel for draw, some gainer, no +buy), I really don't want my deck to be able to hit $8 reliably so Islanding away a Silver (and being vulnerable for one turn to losing one of my own Possessions) is a better risk as then my opponent can at best nab duchies using my deck instead of provinces. An 11 VP swing is big thing.
Certainly, you don't want to blindly stack up on Islands in a Possession match, but you may need to grab an Island just to get rid of one card so you deck is not good enough to gain bonus provinces. Say I use Salvager (which could also be something like Apprentice, Remodel, Stonemason, etc.) to get my deck going and my opponent is using Possession (I'm not), then it is quite likely that at some point he will be able to "trash" a province -> buy a Province. That is going to be a much bigger thing for him than whatever I might trash. So I then buy the Island and halve the utility of a Possession play. Sure anything else that can trash actions is also an option (besides the card I want to nuke), but it might have its own problems (e.g. Trade route might actually be worth $3 coin for him when he "trashes" a province and I have nothing I can trash), it clutters up my deck, and it doesn't give me VP - and of course Island is likely the only other option on a lot of Possession boards.
Possession is screwy enough that when Island is helpful, it is
really helpful and when Island is bad it is
really bad. When I need to get below $8 (so mass Possession doesn't quick buy six provinces), Island works to do it. Similarly when I need to use a scaling TfB early and need it gone late, Island really works. Timing is also a non-intuitive thing - when you want Island is really game state dependent. Slowing down to hide your Salvager has its own risk as now you can't burn a province/buy a province. Possession is perhaps the strongest case for when hiding a card is valuable (because the card in your deck can be SO much more valuable to the opponent), but also one of the times when it is riskiest.
On net, meh, maybe its a wash, but I think when to buy/not buy with Possession is pretty interesting and relevant strategy.