Guild Wars 2

Pretty self-explanatory, yes give the option to merge Mawdrey II, Star of Gratitude and Princess into one. But what could be the 4th converter? Doesn’t have to be it could just be a Gift of Ascension or something like that.
But if it has to be a 4th converter then I guess best would be Karmic Converter – because it’s completly useless. Seriously I only buy something from it once in a blue moon. Unlike my Fractal Reliquary from which I buy almost daily, but using it as the 4th would be a bad move obviously.
The Karmic Converter seems most similar to the Sentient Singularity as both use a common and easy to get currency. Except the part that the Karmic Converter can only be used once per day, while Sentient Singularity up to six.

Now I know what you are thinking; What about Herta? Well can’t do that because it’s a HoT only converter while those are from core game, so it has to be another core converter used.

There’s also the Ley Energy converter, which I use daily to get one of the keys for the HOT chests. But as you say, that’s a HOT converter.

It’ll never happen, but I’d love to catch… I mean, merge them all. (One converter to rule them all! Precious!) The existing singularity multi-converter could be changed to accept all the other converters – even the HOT ones if you have them. And renamed to something like the omniconverter, or multiconverter, or converter tome. Or maybe the Codex of Conversion™. I’m salivating just imagining this. I could put the omnicon in one of my shared slots. Mmmm.