Well the first expansion obviously 
And now I remember the name âBranch & Clawâ
It adds 2 Spirits and a couple of mechanisms:
- event cards that play out just before any Fear cards would and mostly bring complications to the game. But for an easier game one could absolutely curate those a little to get rid off the worst events. (Havenât done it and may have yelled at the deck)
- 4 Types of tokens that go on the map. 3 of them deal with different invader phases: the green wild tokens prevent exploration. The yellow âsicknessâ tokens prevent building. And the blue âstrifeâ tokens prevent fighting. The fourth token are beasts that roam the land and potentially eat the invaders. Yay.
The two spirits are specialized in beasts and wilderness tokens respectively. They are very fun to play. My favorite 2 spirit setup has to be Thunderspeaker and Keeper of the Forbidden Wilds.
There are probably also some more opponents and scenarios in there. I havenât kept track which was added in which expansion. Perplexity says: the only opponent added is France, which I have never played against. There are a bunch of scenarios but I barely ever play them. Heart of the Island is a good one I tried.
The cardpool obviously also grows to include cards that deal with tokens. But it grows with every expansion and I have no particular favorites.
After Branch & Claw, came Jagged Earth which is the next one I would recommend. But really with SI just go in order of publication.