The building completed in 1888 in Mumbai that famously fuses Victorian Gothic Revival with traditional Indian architectural elements is the Chhatrapati Shivaji Maharaj Terminus (CSMT), originally named Victoria Terminus (VT) after Queen Victoria.

Key facts that make it the answer:

• It was designed by the British architect Frederick William Stevens and took about a decade to build, opening in 1888.
• Its style is a striking blend — pointed arches, ribbed vaults, stained glass, gargoyles and a great central dome from the European Gothic tradition, combined with Indian motifs, ornamentation and craftsmanship executed by local artisans.
• It was inscribed as a UNESCO World Heritage Site in 2004 and remains the headquarters of the Central Railway and one of India's busiest stations.

The other options do not match the description or the date:

• Rajabai Clock Tower (completed around 1878) is also Venetian-Gothic in style but is a university tower, not the building of the given year, and is not the standard answer for this Indo-Gothic railway landmark.
• Bombay Town Hall (1833) is neoclassical, with Greco-Roman columns rather than a Gothic-Indian blend.
• Gateway of India was completed much later (1924) and is built in the Indo-Saracenic style, not Victorian Gothic.

Thus CSMT is uniquely the 1888 structure combining Victorian Gothic with Indian elements.