Different Terminal Check In
 

Need some help with this as I couldn't find the answer anywhere.

Myself and my wife are travelling via Changi to 2 different destinations. She will be travelling from T3 while I will be travelling from T1. I will be the only one with luggage. So she will not need to pass by the check in desk if she online checked in.

Is it possible for her to go through immigration from T1 then transfer via the airside skytrain to T3? Or does she need to pass immigration only from T3?

Not a problem. Unless something has changed recently you can both clear passport control at T1 and then she can make her way to T3 once airside. If she doesn't mind walking I would even skip the skytrain and make my way on foot as the skytrain is mainly handy when moving between T2 & T3.

Last time I did this, yes it was possible. However, there was wrinkle.

At that time, (a few months ago), non-check in staff issued boarding passes (kiosk printed/home printed/mobile printed) needed to be authenticated by (1) the airline either manually (a stamp by the airline’s check-in counter agent), or (2) via an electronic reconciliation system which the airlines must be subscribed to. (Note that such a subscription may only be for the terminal they are operating from). So it may depend upon the airline. I'd contact the airline that is departing from the terminal you don't plan to enter from landside and check with them as to what the procedure is for the terminal you intend to go enter airside at.

I remember that in my case it was only the security guard (who pre-checks your BP before allowing you to proceed to passport control) who noticed this and reminded me that my flight is from a "different" terminal. I mentioned that I am aware of this and that I am going airside here because I'm with a friend who is departing earlier than me, after which I will proceed to my own gate. Guy just waved me through.