Can't quite work out which synth you mean. Could you be more specific please?

I'm still a little confused as the arp sound comes in from the beginning, with only a change in melody at 0:18. Is this what you mean? Alternatively you could mean the other plucky synth, which seems to only be playing a single note over and over, which also comes in at 0:18. Which of the two are you referring to?

I waited to post because I wasn't sure what you were referring to. It's the little top line arpeggio pluck that comes in at the start of the new phrase.

I can hear two distinct layers - the tonic root, and a percussive click that goes off into some OTT'd reverb - that's what gets you the sort of high pitched water droplet sound. Would need to actually go in and dig around to figure out the exact sounds, but if I can get it right I'll let you know.

The sharp stab sound that hits before the actual notes is achieved by adding a mod env to all of the oscillator pitches. Then add a slight bit of decay to the mod env (<150ms) and add a bit of reverb to the end of the chain.