Pagarruyung offers a unique experience as being the only Buddhist country in the Indonesia region. It starts as only a minor power in the Indonesia region.
Pagarruyung's idea group focuses on trade improvements, as well as religious and national stability, helpful for an Indonesian nation that is religiously isolated and that will be expanding quickly. Pagarruyung's starting Merchants can be placed locally for the moment, but should be sent to the Canton and Hangzhou nodes as soon as they come within Trade Range, as these nodes normally require a Merchant to route their value towards the Malacca node.
In most games, 马六甲 will rival both Siak and Pasai despite sharing religions with these nations, due to their border friction. It is very likely that some of these nations will also rival Pagarruyung, but each nation will be easier to defeat if they do not have local allies available. However, the small nations of 吉打 and 北大年 may find allies in Pagarruyung's rivals, and these nations are not trivial threats for a three-province nation such as Pagarruyung.
From day one, begin improving relations with 巽他, or 马六甲 if they did not rival the player. Either nation should accept a royal marriage fairly soon but getting them allied requires some time spent improving relations. If available, a Diplomatic Reputation advisor can help to acquire allies sooner rather than later.
Another excellent ally to obtain if possible is 阿瑜陀耶; due to Pagarruyung's size, this may be difficult, but Ayutthaya does share religions with the player's nation and so the alliance may be possible with time. 高棉 is likely to be attacked by Ayutthaya early, making them a poor choice of alliance unless they are victorious somehow.
As with all nations, it is recommended to build up to the starting Force Limits in both Army and Navy, so as to discourage attacks by enemy nations. Pagarruyung's Gold province will account for a significant portion of initial income, but the player may lower army maintenance slightly and mothball their unused Transports if the player is willing to take the risk of an attack in exchange for a better economy. While doing so, the player should fabricate claims on both of their neighbors, particularly Siak.
Even if all of the above is accomplished, Pasai might still decide to declare war. Without a decent ally, this war may be impossible to win unless the player invests heavily in loans and hires mercenaries far over the Force Limit, especially since Siak is likely to opportunistically declare war as well. However, if everything goes as planned, Malacca or another nation will be an ally, deterring attacks long enough for claims to be prepared on Siak. As soon as possible, the player should declare war on Siak, calling in their ally if necessary, depending on any defensive alliances Siak has formed. Vassalization of Siak is an option as they are a Sunni nation that contains no essential local provinces, but Pagarruyung also desperately needs more land at this stage of the game. If the player choose to create a vassal, caution must be used to avoid a dangerous disloyal vassal, usually by annexing one province from Siak and vassalizing the remainder.
If vassalized, the player should improve relations with Siak to lower their liberty desire as well as begin fabricating claims on Pasai. When an opportunity presents itself, the player should attack Pasai, again possibly with an ally's assistance, depending on the quality of Pasai's defensive network. If successful, the player can then divide lands between Siak and their own nation, but Pasai province itself (2673) should be annexed directly due to containing a Center of Trade.
Next steps: Exploration and Forming Malaya
Getting Exploration ideas as soon as possible is a strong option for the Pagarruyung player, as colonization is needed to eventually form 马来亚. The uncolonized provinces in Indonesia are also quite rich and are ripe for the taking.
In order to form Malaya, control over either Borneo or the Malaya Peninsula is required (in addition to Sumatra), as well as four provinces on the island of Java. If Pagarruyung remains allied to Malacca, the player can choose to replace them with Ayutthaya and then annex their former friend, taking control of the Peninsula for themselves. However, the player should beware of betraying Ayutthaya if they were promised territory. Remember that control over the province of Pattani (594) is required in order to fulfill the requirements for this region, but Kedah (2394) is not.
If the player wishes to maintain the alliance for the moment, Pagarruyung will need to colonize in order to fabricate claims on the other nations in Indonesia. The province of Belitung (2679) is useful for claiming land in Sunda or Majapahit, whereas Pontianak (640) can be used to claim parts of 文莱. In addition, both provinces are necessary to complete official control of their respective islands. Whichever choice the player makes, these regions can often take multiple wars to conquer completely, due to the development of the provinces and the fact that Majapahit and Brunei are likely to annex their smaller counterparts, making the wars more difficult to win.
In addition, Australia can make a suitable area to colonise early in order to form a Colonial Nation, while the Philippines offer some very high development provinces and are important to seize before the inevitable European colonizers. The Andamans can be useful to fabricate claims to the player's north if expansion into India is viable due to a weak Bengal.
The Late Game
After forming Malaya, the player can take several different courses. Conquering Buddhist land from mainland nations in Indochina is a strong option that can bring significant Trade Value back to the Malacca Trade Node. Alternatively, control over nodes in northern China such as Hangzhou and Japan can allow the player to route trade from Colonial Nations in limited areas of the New World, specifically Mexico, California and Rio Grande, back to Malacca as well. If a Random New World is selected, significant amounts of New World trade can flow through the Philippines or even Australia, making control over these areas even more valuable.
Normally, despite the player's best efforts, European colonizer nations will eventually gain a foothold in Indonesia. To prepare for the arrival of the Europeans, the player should take steps to remain as advanced as possible in Military and Diplomatic technology as well as searching for allies with powerful navies, such as a united 大明 or a powerful Indian Sultanate, such as a successful 毗奢耶那伽罗. The natural wealth of the Indonesian archipelago should assist the player greatly with this challenge.
Though Exploration and Expansion come highly recommended, many different idea groups are strong choices for Pagarruyung. Trade and Maritime ideas are useful to gain further economic benefits from the rich Malacca trade node, whereas Naval and Quality ideas are sensible choices for balancing the scales against the Europeans at sea.