All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Hellfire is constituted of downward grades as
As regards supplicating against the enemy to enter Hellfire, if what you meant by enemy is the non-Muslims, then it is stated in the Quran that it is permissible to supplicate against them. For instance, Moosaa (Moses) and Haaroon (Aaron), may Allaah exalt their mention, supplicated against Pharaoh, the enemy of Allaah, and his people. Allaah Says [speaking on behalf of Moosaa ] (what means): {"Our Lord, obliterate their wealth and harden their hearts so that they will not believe until they see the painful punishment."}[Quran 10:88].
Furthermore, Imaam Ahmad reported that on the day of the battle of Uhud when the non-Muslims retreated, the Prophet said: "Straighten your lines so that I may glorify my Lord", so he supplicated for a long while and said: "O Allaah! Kill the non-Muslims who deny Your Prophets and hinder men from Your Path, and inflict on them a severe and painful torment." It is also confirmed that the Prophet supplicated against the non-Muslims on the day of the battle of Al-Khunduq (i.e. the trench) and said: "May Allaah fill their homes and graves with the Fire as they distracted us from the middle prayer ['Asr] until the sun set." [Al-Bukhari and Muslim]
Allaah Knows best.