roliloipo said:

Can someone explain to me how the relic islands work. Thank you in advance because most likely I won't reply to say thanks.

I am happy to explain it, but you'll need to tell me what are you really asking about: treasure islands, as your title suggests, or relic islands, as your messages claims? Both can be found in your lighthouse (or directly on the map), but they are under different tabs and they are very different in how they function.

In order to get a relic from a relic island, you have to capture it and hold it. Unlike TIs, you can do so with any units (no need to send off AND def). Also, unlike TIs, all the units that you send will participate in the fight (in case someone is on it) and you can hit it even if't held by your BH mate. Another important difference is that the units returning from a relic island will never auto-turtle.

As you're sitting on it, your chance of getting the relic improve with time. You decide when to claim, and then you either get a random one or you don't get anything. This is when your aforementioned chance kicks in: if you claim as soon as possible, you probably won't get one. If you wait the full time (there is a progress bar, IIRC), then you have a high chance of winning (it never gets certain).

In my opinion, the relics are not worth it. Most of the useful ones are obtained in battles, and the res value of any one you don't want to keep is ridiculous (3x3k res is the top price I've ever seen). I also think that many players agree with this, because I haven't seen a fight over one since the TIs were introduced, and those few I've hit since only had a single Bonnie or something similar there.

So, if you see one open, claim it with a few Bonnies and let them sit there max. time. Then (attempt to) claim a relic and let the Bonnies sit some more for the next claim. If you get knocked off of it, no harm done really.