Wahdal al-Wujud (THE UNITY OF EXISTENCE): The most evil believe of all. This means that only Allah exists and the rest is nothing. In other words, everything is Allah and Allah is everything – the man, the donkey, the monkey, the tree etc.
Wahdal al-Wujud (THE UNITY OF EXISTENCE) means Allah is present in everything. And Wahdat ul Shahood (APPARENTISM OR UNITY OF WITNESS) mean all things are reflection of Allah.
Wahdal al-Wujud (THE UNITY OF EXISTENCE) means the unity of being/unity of existence. Doctrine formulated by the school of Ibn al Arabi, which postulates that Allah and His creation are one, since all that is created preexisted in Allah’s knowledge and will return to it.
While,Wahdat al-Shuhud (APPARENTISM OR UNITY OF WITNESS) is opposed to Wahdat al-Wujud (THE UNITY OF EXISTENCE). Doctrine taught by Sufi Ahmed al-Sirhandi which holds that Allah and His creation are entirely different.
Both doctrines are related to the relationship between Allah and the universe.
1-WAHDAT UL WAJOOD (THE UNITY OF EXISTENCE) or Sufi Doctrine means that only existence is of Allah and everything else is dependent upon Him. Or they say it is Allah that exists in everything and this whole universe is a mirror of Him. It came out of the belief that only Allah has to live forever and he is independent while every other thing of this world is dependent on Him.
2-WAHDAT UL SHAHOOD (APPARENTISM OR UNITY OF WITNESS) is opposite of the above doctrine (which basically emerged out of the danger that common people could possibly forget any differentiation between Allah and His creation, which Sufis infact said due to their ultimate love with the Creator and does not actually means that Allah and Creation is one, it just meant that Allah and Creation is very close to each other) and it says that Allah and His creation are separate and nothing can be merged with Allah.