Is it possible to get admission in M.S in US for mechanical with a low aggregate score and GRE?

No, GRE is not mandatory for all universities. Top institutions like University of Toronto and UBC often require. Many universities like Simon Fraser University, Ryerson (TMU), and Carleton University make it optional or waive it if you have a high GPA and relevant work experience.

Candidates with a valid score of CAT/ GMAT/ GRE score are exempted from the written test. These candidates still need to complete the form by paying the application fees. However, these aspirants may get called for the IIM Trichy - Chennai campus PGPBM interview round. 

The University of Buffalo ask for GRE score for some PG programs. The university provides test option for international students. Students usually submit these score along with the transcripts, LOR, English language requirements to give a boost to their application.

It depends on country you are applying to. Top US universities usually require GRE scores. UK and Australia often GRE waive off. Always verify specific eligibility of university you are applying.

No, students don't need to submit either a GRE or GMAT score for most GSU courses. Business programs offered by the Robinson College of Business, have waived off the test score requirement for most courses.

However, students applying for studies at the Georgia State College of Law, may have to submit a valid GRE or LSAT score for courses like JD.

Students still can submit a valid score in either test. This can certainly have positive effect on the overall application.