To bring Mark/Chelsea to the Island, you need at least 50% completion and you need to have brought all main characters to the Island. You therefore need to have unlocked all areas on the map as well as having visited them. You need to have met all the Characters, including the Harvest Sprites who act as the guardians of each area. Some players had not been able to unlock Mark or Chelsea even when these conditions were met. A 'hidden' requirement does exist, and I suspected that it might be simply a requirement in terms of total Farming Degree points.
In Island of Happiness, new options usually are unlocked by one of the following:
1. the arrival of a new Main Character;
2. the arrival of a new subsidiary Character;
3. shipping a required number of specified Crops.
The basic requirements for bringing Mark or Chelsea to the Island are approximately 50% completion as well as having brought all Main Characters to the Island and to have met all of them, including the Harvest Goddess by throwing an offering into her Spring. You need to expand the Hotel as well because that is where Mark/Chelsea will live.
A player left a comment to the effect that it may be related to Festival attendance which made perfect sense, but in fact, was disproven by players who managed to unlock the arrival simply by completing the original requirements of bringing all main characters to the Island and unlocking all areas. Other players had thought it was related to the ownership of ranch animals, which was logical but now has been proven to the contrary. A player with no animals apart from the horse was able to bring Mark/Chelsea to Sunny Island.
I would like to thank all players who wrote about their Festival participation, by the way. It is only when many players write about their game experiences that hidden requirements can be proven or disproven.
Now, however, there have been so many different combinations of events that have served to unlock Mark or Chelsea that it is evident it can be only one true requirement: current Farming Degree points.
Everything else in Island of Happiness is based on that variable, after all. Farming Degree, Farming Degree, Farming Degree: whether it is the colour of a Wonderful, the appearance of a Wonderful or the 'hidden' requirement for an Event or arrival of a new character. It always is proven ultimately to be related to the player's Farming Degree total, a variable based on every aspect of life in Island of Happiness.
I therefore will strike ALL specific 'hidden' requirements for the arrival of Chelsea or Mark from my guides now. Every player fulfills the 'hidden' requirement differently, because it is nothing more than total Farming Degree points. What would be most useful now is for players to tell me what their Farming Degree titles were when Mark or Chelsea arrived for the first time. Although you cannot see your precise point total, you CAN see your current Farming Degree title in your Menu.
All aspects of life in Harvest Moon are vital. You need to farm, ranch, fish, mine AND make contact with every one but finally, ship items regularly in order to maximise your success. Unlocking new options, arrivals and Events is linked not only to farming, ranching, mining and fishing but to SHIPPING as well.
In terms of the final Rival Heart Event that will allow a Rival couple to marry, there evidently are specific aspects of life that are linked to this Event.
I was able to trigger Denny's 4th Rival Event only when I began to fish again after neglecting that aspect of my life for a season or so. Another player was able to trigger Vaughn's 4th Rival Event after mining again. Obviously, Elliot's 4th Rival Heart Event would be connected with farming. Rival marriages therefore are linked to specific activities. Vaughn is not involved with mining at all but Sabrina is. Both Lanna and Denny are involved with fishing. I wonder, though, if there is a ranching requirement to be met as well in terms of Vaughn's 4th Rival Event as he is connected with Animals. Julia likewise is connected with Ranching.
You don't have to be aware of these requirements if you are performing all activities and shipping items in every category regularly. I always ship a fair number of Ranch products processed through the Makers as they are linked to subsidiary characters... so I would not know if this were a requirement in the case of Elliot and Julia's 4th Rival Event or Vaughn and Sabrina's 4th Rival Event. I would be very interested to hear from any player who had shipped the required number of ores for Vaughn/Sabrina's 4th Rival Event and yet had no animals or had shipped no Ranch Products recently and therefore could NOT trigger the Event. I would be interested in the same situation with respect to Elliot/Julia's 4th Rival Event...
In other words, does the Event have requirements solely where one partner is concerned or for BOTH the Rival and the Eligible Bachelor/Girl?
Each day, I marvel at the complexity of Island of Happiness as new situations uncover another twist or turn in the game...
Note that many new options are linked to the Subsidiary Characters in Island of Happiness. These Characters often are referred to as members of different teams, such as the 'Farming Team', 'Ranching Team', 'Fishing Team' and so on, although they each come to the Island for different reasons and operate independently of one another.
In order to unlock new farming options, you need to bring members of the Farming Team to the Island and by completing farming goals, you will bring new Farming characters to the Island. The same holds true with respect to Ranching options and the Ranching Characters. For example, players who have been unable to unlock a Sheep will discover that bringing more Ranch Characters to the Island is the solution. Thus, all aspects of the game are connected.