Shun- if someone has done something wrong, that goes against the beliefs of a community or belief system, they get shunned. Avoid- you do all of can in order not to do something or see someone. When it is hot I avoid walking in the sun. Or I avoid him, because he is nasty. Halt- means to stop smth. „Halt the proceedings“. Based off is basically exactly the same as based on. Any difference in usage would just be semantics.

Shun is to notice something, unsually that you don`t like or want to deal with (it can be a person) so you just sort of ignore it, or pretend it or the person doesn’t exist. Example. Some churches say to „shun“ members who leave, not talk to them and ignore them. Avoid is just stay away from something unpleasant (I avoided the accident on the freeway and the traffic jam it caused, by taking a side road). Halt means just to stop. He was halted by police. The word has a kind of limited use. You can halt someone, but only when they are in motion. Halt is often used with other words to show you`re bringing an end to something (not in motion). Like, „to put a halt on“ something. Like he put a halt on his drinking. You can`t say „he halted drinking.“ You can halt a horse, but most would say „bring the horse to a halt.“ Halt usually needs a little more to it to make it work, but if I said it it would only be like to „pull someone over“ (like when driving in a car). The police might make you halt for a moment for something. Based off is very common. It means coming out of something, being the result of something. A new TV series can be based off an older successful one for example. So, you could say „that show is based of the XYZ show.“ Being based off something just means having a foundation in something, or having gotten a start because of something that laid a groundwork of sorts for something.

David has a great explanation of the differences between 'shun', 'avoid', and 'halt'. 'Shun' is normally only used for people and social situations. I'll also add that, in my opinion, 'based off' is much more informal and colloquial. Otherwise it has the same meaning and use as 'based on'.

2) based off and based on have the same meaning

1) Shun is a stronger version of avoid, but mainly used for talking about people and not common in everyday conversation. Halt means to stop.