Zaginiona wyspa Arnak

No — a card can be used either for its travel value or for its effect, but not both; choose one when you use the card. (Rulebook, p.8; p.13)

The guardian has no immediate effect when placed; however, at the end of the round you gain a Fear card for each archaeologist you take back from a site that still has a guardian on it. You can overcome the guardian later as a main action to avoid that Fear and gain its boon. (Rulebook, p.10–11; p.17)

You can cover a two‑icon cost using travel values from two sources (two separate cards) or with a single card that itself provides both icons; a card that provides extra icons can also overpay a one‑icon cost but the extra icon is wasted. (Rulebook, p.9)

Assistants are exhausted when used and normally refresh (become available) at the end of the round, but when you upgrade an assistant to gold you flip it and it is refreshed immediately, allowing an immediate reuse. (Rulebook, p.16)

Passing is your main action and you should use any free actions you still want before you pass, but you do not take back archaeologists or resolve guardian Fear until the end‑of‑round setup when all players have passed; archaeologists are returned simultaneously then and each return from a guarded site gives a Fear card. (Rulebook, p.17)

Yes — when you buy an artifact you move it to your play area and may immediately resolve its effect while ignoring the artifact’s normal play‑cost in the corner; playing that same artifact later from your hand would require paying its play‑cost. (Rulebook, p.12; p.13)