Algorithm creation is something of an expert-level task, so we have little basic information. If you haven't already, try the following:
Programming Manual for Harmonizers
https://www.eventideaudio.com/downloader/1007
Omnipressor: Anatomy of a Preset
https://www.eventideaudio.com/downloader/7340
Once you have moved on from these, try picking a few factory presets that look useful, and take them apart and see how they work.
Your synthesizer should be do-able, with PITCHDETECT, OSCILLATOR and MIXER. But, the skill will be in making it playable.
