Other events : the most expensive ones (lost arts, inheritance, pathfinding) seem obvious but is it reliable ? If you manage to hit $9 first turn you can buy a $5 card + mission, and then you have to be confident that you can hit $7-8 on your Mission turn to get that Pathfinding.
Mission VS outpost : well, Outpost is way better (buy it only once) when you can refill your hand in a reliable way. Some cards help you to do so : Scheme, Guide. There are also obvious refillers (Watchtower/Library, Menagerie, Minion too) but you still to get them in hand. However, it mostly requires the ideal cards (guide is the best !!!) or thin trashing.
This is why Mission is still better when you don't have these. And generally, you know when you should buy missions, that is when you know you'll likely remodel that Gold into a province this turn, or just buy another mission. Also, Mission has the advantage not to hurt your deck but the disavantage of having to be paid multiple times. So it's more flexible, moreover it's easier to afford.
All in all, they are very different. But there's a 3-turn combo not to forget (from DominionStrategy Wiki : If you resolve Outpost first, you get the normal 3-card Outpost turn, then your Mission turn, giving you three turns in a row.). Can be helpful sometimes. Unfortunately, it's not as great as if you could preparing your outpost turn with your mission turn, plus it requires an engine, and cash !
Best cards to play :
Trashing cards (especially Remodel-> Province) I talked about are truly the best ! Salvager is quite bad, however.
Duration cards (Seaside or permanent) can be good too, mostly Tactician !
Where are they walking : I assume the guy (girl ?) who holds the flag is statistically right-handed and therefore walks away.
