Slander the Buddha, the good Dhamma, what is proper and right, and the carrier of such and their deeds, the Noble Ones, requires wrong view and such strong wrong view will definitely lead to hell. More about critic and praise in AN 4.83: Avannaraha Sutta - Dispraise and see also Respect and Veneration
But it does not stop here. Even if slandering a worldling, yet a giver, person of goodness, one one owes gratitude, such as father and mother, teacher, leader of ones community, recluses... also such leads to hell and if gaining a human existence he/she is not influential wherever reborn, he/she is low-born wherever reborn. The Shorter Analysis of Action.
Note and worthy to think about is that physical action might have there effects quick but it is based on mental actions, thought, that has the most impact for a long term, and so even if not spoken out, not physical acted, just thinking "idiot" can have a lot of impact if matching the well gone and well going.
One who tells lies (about others) goes to niraya; one who has done evil and says "I did not do it" also goes to niraya. Both of them being evil-doers, suffer alike (in niraya) in their next existence. DHP
[This is not given for trade, exchange, stacks, Buddh-ism but for release. For further questions on it or if seeking space for talking about, one may use this exit •]