Transfer at SIN on two different tickets
 

Dear Changi experts:
I'll fly SIN to MUC on SQ soon, leaving at 00:25. It now happened that I will be in Bali the days before, i.e. flying into SIN the evening before on a separate ticket. SIN to MUC will be in C, DPS -SIN in Y.

Options are:
SQ/MI arriving at either 15:35 or 22:40, obviously no flight in between. Probably the easiest connection as I'd expect them to check my luggage through and a certain likelihood of no terminal change. But 15:35 would mean a really long transfer time, while the later flight would not leave much time to explore lounges and so (will be my first time in C out of SIN).
KL arriving at 21:25, good price, but a game of luck whether they will check the luggage through and change of terminal, but T1 to T3 shouldn't be too difficult.
GA arriving at 18:20, again maybe the need to clear immigration and re-check baggage, but no terminal change.
Air Asia, arriving at 20:15 or 20:45, good price and good schedule, but probably the least convenient transfer. Travel will be in September and I'd expect them to arrive at Terminal 4 by that time.

I'd appreciate your thoughts and advice on how to make the connection. Main concern is of course reliability as I must not miss the flight out of SIN, followed by convenience.

Changi offers easy and fast terminal transfers. With that being said, forget AirAsia. No through-checked bags with them. You'll have to retrieve bags then clear customs (super fast), then check your bags with SQ. Not good. KL and GA will through check bags to your final destination from Bali. If I were choosing, the KL flight hits the right notes. Good departure time out of Bali, competent airline, good arrival time in Changi with plenty of time to hit the SQ lounge. Wish you luck.

With a separate onward ticket on a different airline? - I don't think so. It might be possible with SQ DPS-SIN, but not the others.

You might consider either Tigerair or Jetstar Asia. Both are low cost carriers.

Tigerair: is part of the Singapore Air group. If the Tigerair flight is part of your overall SQ itinerary and purchase Tigerconnect this will allow direct transfer of your luggage, you won't have to enter Singapore legally, pick up your bag at the carousel and recheck in. The bad news is that the two Tigerair flights are not convenient. One arrives at 13:25, the other arrives at 21:45. Tigerair uses T2.

Jetstar Asia: is part of the Qantas group. They have one flight which arrives SIN at 17:10. They won't interline so you will have to legally enter Singapore, pick up your luggage and check in at SQ. Jetstar uses T1, you'll have to go to either T2 or T3 for SQ.

According to Wikipedia https://en.wikipedia.org/wiki/Singap...ort_Terminal_4
neither Tigerair nor Jetstar are currently on the list of airlines making the move. Personally I doubt either airline will, my guess is so that passengers on these airlines can more easily connect on SIA and Qantas flights respectively. It is also worth knowing that T4 will not be part of the internal people mover system but will be connected to T1/T2/T3 by a shuttle bus so the transfer to that terminal won't be quite that fast or easy.

I would do Jetstar because the timing would suit your needs better than the other choices you investigated.

I wouldn't expect to be able to check bags through on separate tickets, especially if the airlines aren't partners or one is a LCC. However, the transfer desk (airside) at SIN might be able to retrieve your bag and tag it for the SQ flight, so that you could avoid going landslide to check in.

Don't worry about changing terminals as SIN is really one big terminal with different zones that were build in phases. There's an airside little train/tram or you can walk, although the tram is infrequent in the middle of the night.

Similarly, even if you must enter and go landslide to retrieve and recheck the bag, it's not a big deal. This is an efficient airport. More importantly, since you're departing on SQ, you don't need to wait for their check in counter to open. You can check in at the airport starting at T-48 and then go airside to enjoy the airport: free movies, the butterfly garden, koi ponds, lots of shops, interesting F&B outlets, as well as the excellent SQ lounges with very nice showers as well as F&B. There's even a big slide (fee to use), IIRC landslide in T2.

It sounds like you don't want to explore downtown, but nevertheless, I'd still allow lots of extra time because you have two tickets. I also would avoid a carrier with once a day service DPS-SIN unless they interline with other airlines. This would exclude some LCCs from consideration. It's not worth risking a long haul SQ J ticket to save a few dollars.