R. Eric Reuss
Event Cards are part of the Branch & Claw expansion, which was only split out from the core game late in development (for reasons of cost and learning-complexity). While you're learning the core game, Events are an unnecessary distraction, but once you're familiar with Spirit Island they do several very good things for the game, both mechanically and thematically!
You can see a sample Event Card at right. You draw one each Invader Phase, and most make three things happen: one of two Main Events at top; a Token Event underneath it that deals with Beasts, Disease, or (rarely) Strife; and a Dahan Event at bottom - the existing human inhabitants of Spirit Island taking some action.
Events didn't exist in the early prototype versions. So:
There were (initially) two driving factors:
Mechanically: The core game of Spirit Island has very little random chance. The only major sources of uncertainty about how the board will unfold on a given turn are "Where will the Invaders start their Explore-Build-Ravage cycle next?" and "How will the Invaders panic if we've earned Fear Cards?"
So as you play more, you start to be able to predict victory further and further ahead of time. Eventually - and the number of plays I'm talking about here varies a *lot*, for some players it's 5-10 games and others it's 40-50 - you can sometimes foresee wins with near-certainty 2+ turns ahead of time, which drains the tension out of the endgame. It can still be fun to stomp on Invaders, but it becomes a lot less engaging when you know you've got it in the bag.
The Event deck introduces a bit of uncertainty, a jitter in that mental needle tracking likelihood-of-win. The Event Cards average out to something near neutral-benefit, but they can alter many details of what transpires... and not knowing those details transforms "We're certainly going to win in 2-3 turns" into "We've got a good shot at winning in 2-3 turns", and that makes all the difference in terms of game interest.
(But with new players, that jitter is bad: they're still learning the basic dynamics of the game. Per-game variation just makes it tougher to learn.)
If you're about to lose, Events also hold out a glimmer of hope that perhaps you'll survive the coming Invader Phase - though in the core game, Fear Cards often serve that purpose, too.
Thematically: The Invaders are humans, not predictable robots. The Dahan are humans, not obedient minions. The wildest Beasts of the island may make the Invaders' lives difficult (or short), but not in an organized way. In short, there are many living systems on the island, and living systems tend towards the messy and unpredictable. An Event deck creates that unpredictability, that sense of life and wait-you-did-what?
As I implemented Events, I found some other benefits: The token events let Strife, Disease, and (especially) Beasts interact with the board in a variety of ways, expanding and refining their effects without adding any additional rules overhead. It's highly in keeping with the theme for the Invaders to pull unpleasant surprises from time to time: the Spirits are for the most part slow and reactive, the Invaders faster. And the game's a lot more tense when leaving 1 Explorer in a land about to Ravage is very likely to be safe, but not 100% guaranteed.
I also found - the hard way, over and over - that some sorts of Events were just un-fun: for instance, anything which subverted the usual Invader Action progression too heavily undercut the core strategy of the game. Learning to distinguish "this Event is painful and makes the game harder" from "this Event is painful and makes the game un-fun" took some time, especially as some were only ferociously un-fun one time in four.
Not all the Events look like the one above. Some offer a situation with a choice to be made, like at right. A choice may have costs associated with it, or not, but the two options always have rather different consequences.
When first making Events, I'd considered including ones based off of mini-stories, but never even tried prototyping it - I felt like there just wasn't enough space on the cards to make it work. Playtesters kept bringing it up as something they'd enjoy seeing, though, and one (Brian - thanks, Brian!) tossed out a few seed ideas that got me thinking along the lines of crux choice rather than paragraph of narrative. Story was still present, but via the framing of a situation and the choices made in response, not as a long blurb of narrative text.
Some early Choice Events offered three distinct choices, but testing found that was too much for players to keep in their heads - particularly when hearing them read out loud. So they all became A-or-B choices - which may have been for the best anyhow, as card space is limited.
Risks and Randomizers
I knew I didn't want Events to be too predictable, so I made a modest number of the early Event Cards involve a random terrain or a random land#. The cards all had a terrain printed in one bottom corner and a land# in the other bottom corner, for use as randomizers - an Event might say, eg, "Draw a random land#. On each board, add a Town to that land."
I got pushback on this from several sources, most heavily from Christopher of Greater Than Games, who felt both that the extra icons on each card were confusing and distracting, and that the Events which used them were generally terrible. (And indeed, there was a strong overlap between them and the "un-fun" Events mentioned above.) I dropped over half of those Events, and found ways to make the remaining ones work without the terrain/land# randomizers. (Which also made them less swingy.)
Then Choice Events came along. Sometimes, it seemed they would be both more thematic and more interesting when one of the options involved taking a risk.
What proved easiest and best was using the Power decks as a randomizer: you'd flip a Minor Power, say, and check some quality of the revealed card. This can even let the randomization be thematic - eg, in Years of Little Rain (at right), flipped Power Cards that grant a Water element are good, ones without are bad.
There's some chance in how these risks play out - but the tension and theme they add is entirely worth it, and players will usually have the option of taking a risk-free path... with its own costs and consequences.