I passed 12th this year and will give iiser aptitude test next year. Will they take board exam cut off of this year or previous year for class 12 Mark's for eligibility?
yes you are eligible for the counselling in IISER through your examinations. You can defintely give the entrance exam but the only rquirement is to have 75%(genral, obc, obc-ncl) in your 12th board and 65%(sc, st, pwd).
You can visit the official website of IISER to know in detail