2. How/why can you dodge Siren's restriction?
it seems like most people aren't familiar enough with the stop moving / no visiting rules to understand tricks for dodging Siren's restriction. So here's my quick explanation:
(All of the following also applies to dodging Gatekeeper; it's just that uh no one buys that card)
There are 3 different categories of cards that are relevant for the no visiting rule:
1. gain a card directly to a location (Armory, Sculptor)
2. when you gain a card, move it (Siren, Travelling Fair)
3. gain a card. then move it (Replace, Summon)
(For more examples of cards within these categories, http://wiki.dominionstrategy.com/index.php/No_Visiting_rule)
When you have multiple effects at the same time (i.e. category 2), you can order them. So if you buy a Siren, you can choose to topdeck it with Travelling Fair first. And then you resolve the Siren's effect, except that the Siren is no longer where it was gained to (your discard pile), so the Siren fails to trash itself.
I've been thinking about this for now, and I think by myself: is this really the logical route? In particular, it really seems really weird that "when you gain this, put it into your hand" and "this is gained into your hand" aren't functionally identical.
The no visiting rule (which only applies to category 1 if I understand correctly) in particular seems to be designed to be able to use moving on-gain effects on cards that are gained into your hand or onto your deck. So to me, it seems logical to broaden the expected location for gained cards to:
a) Your discard pile
b) Your hand
c) A specified location in your deck (which means that if the gained card entered your deck pre shuffle, it can no longer be moved)
As cool as being able to dodge Siren's restriction with optional topdecking, it is something that Armory and ideally also Replace should be able to do as well if we go for it IMO.
That said, I know I cannot outthink the development team, so I'm pretty sure they have good reasons why it is the way it is now.