Singapore's public transport operates on a continuous journey principle when switching between train <-> bus and bus <-> as long as you use the same payment method and don't have more than 45 min between transfers. And you don't need to buy tourist pass for that.

As an example: if you take a train from Changi to Reffles place, then got out and take #10 bus from Raffles Place to Jurong East, and then hop on another bus from Jurong East to take you to Zoo - as long as you use the same payment method, it would be considered as a single journey and you will pay something like $2.20 for it. Another example is if you take a bus at Botanical Garden going towards Orchard, got out and switch buses three times, as long as you don't have more than 45 min stops between buses, it is the same journey and will be something like $1.

In the past there were cases when I was going from Plaza Singapora to Larkin bus terminal in Johor and the total journey was something like $2.5...