Short answers, pulled from the story.
The Masyumi Party formed in November 1945 following the Indonesian Proclamation of Independence on the 17th of August 1945. Founders included Mohammad Natsir, Mohammad Roem, Sjafruddin Prawiranegara, Jusuf Wibisono, and Abu Hanafi alongside traditionalist and modernist groups.
Masyumi won 7,903,886 votes representing 20.9% of the popular vote for fifty-seven parliamentary seats in September 1955. About 51.3% of the party's vote came from Java while it remained dominant outside that region as the leading party for one third of people living there.
President Sukarno passed a law in 1960 allowing him to ban parties whose ideologies conflicted with state principles or whose members rebelled against the government. The Masyumi Party refused to condemn senior figures who joined rebels in Padang within Sumatran territory in November 1957 which severely damaged its public image.
By 1950, Masyumi had become the largest political party in Indonesia with forty-nine seats in the People's Representative Council legislature. The party played a dominant role in Indonesian politics from 1945 to 1949 alongside the Indonesian National Party and Socialist Party.