Avodas Kochavim 5:4
It is a mitzvah for the target of the meisis to be the one to execute him, as per Deuteronomy 13:10, “Your hand shall be the first against him to kill him.” The target is not allowed to love the meisis, as per Deuteronomy 13:9, “Do have affection for him.” Since Exodus 23:5 tells us to help our enemies, one might think that we should help a meisis. Therefore, the Torah tells us, “Do not hearken to him” (Deuteronomy 13:9). Similarly, Leviticus 19:16 tells us not to stand idly by our brother’s blood. One might think that we may not stand idly by the meisis’ blood. Therefore, the Torah tells us, “Your eye shall not pity him” (Deuteronomy 13:9).
The target is not allowed to testify on behalf of the meisis, as Deuteronomy 13:9 continues, “Do not show him compassion.” If the target has evidence against the meisis, he may not remain silent, as the Torah says, “Do not conceal for him” (ibid.).
The verse that prohibits regular people from proselytizing as a meisis is Deuteronomy 13:12, “All Israel will hear and be afraid and they will no longer do such evil things as this in your midst.”
Avodas Kochavim 5:5
Let’s say that someone proselytizes others by telling them that they should worship him: If he tells them to worship him and they do, he is stoned. If they didn’t worship him, he is not stoned, even if they accepted his words and agreed. On the other hand, if he tells them to worship another person or an idol, then if they accept his words and agree to worship, both the meisis and the target are stoned even if they never actually worshipped. Deuteronomy 13:9 tells us not to have affection for or listen to a meisis; if one had affection for or listened to him, he is liable.