You may be surprised, with some studying, you would have found that this AHC, was completed by otl.
While I typically classify most of the Ghulat or more radical Shi'i groups, usually belonging to the Nizari, as more influenced by Greek philosophy, the old cults of the Roman period and Manichaeism, the two examples I have of major Islamic and Zoroastrian mixing creating legitimate sects would be as follows:
The Khurramiyyah, a radical group of formerly Zoroastrians in Zanjan and Gilan during the 800s-900s AD. While being nominally Zoroastrian, they in my personal opinion, resembled more a mix similar to the later Qarmatians. Which is; a mix of Zoroastrian concepts of society and dualism and time periods mixed with the hero worship, radicalism and communal lifestyle of the Ghulat (the exagerrators). This within the Khurramiyyah led to a relatively liberal society in terms of social standard, extreme faithfulness (as in, they were fanatical in their cause, to the point of suicide) and a sort of village anarchy within the hills of Zanjan.
The other, more substantial example:
The Qarmatians (the ones who write in small figures/letters), a group from the 900s-1100s. They as a group held several distinguishing features from Shi'i Islam and others (they are considered Is'maili-Nizari):
1. The belief that every time period has a messenger or prophet and that that prophet is Allah or his image. Whilst on Earth the person, was the incarnation of Allah, in his image. This was started with Adam to Zoroaster to Jesus to Ali ibn Talib to then who ever. This was called at the time millennialism or the belief that every millennia had a prophet and was popular among Ghulat of the time period.
2. However, despite the millennialism of the Qarmatians being similar, it was the most radical of all the Ghulat in this form. They essentially believed, that every millennium did not have only its own prophet but its own religion and morals, that even millennia replaces a religion with another and a moral for another, thus to them, religion was ever changing and revolutionary.
3. To further that point, they said that each age repeats itself and everything is like another but with different characteristics. So to them, the past age was the exact same as the current but with a different face.
4. The Qarmatians held the stars as the heralds of Allah's will. This is characterized by their attack on Makkah which was done due to the lining of Jupiter with Saturn and the 1500 of Zoroaster. This is an obvious Zoroastrian or called then, a Majoosi (Magi) influence.
5. The Qarmatians held that Ali ibn Talib was the true messenger and thus Allah and Muhammad was a liar. This is the major characteristic of the Ghulat and the original teaching of Abdullah ibn Saba.
6. The practice of vegetarianism and respect of animals.
7. That fire was the representation of Allah's will, brought from the Majoos, as in Sunni or other Shi'i, the representation of Allah is nothing but the Quran (assuming they are not Ghulat, as well).