Ice nihil icyenic creature created by the god Zaros through genetic experimentation with Icyene and are first encountered during Fate of the Gods.
Nihil are one of the most powerful non-boss monsters in the game and you must be well prepared before fighting them. They have very high defence and extremely accurate attacks and therefore it is recommended to use stat-boosting potions and/or prayers to break through their defence and increase your own. It is also highly recommended, if not required to wear the Shard of Zaros when fighting the Nihil as they are aggressive without it and you will be killed very quickly after being attacked by all of the Nihil in The Pit. Furthermore, each Nihil is capable of using a special attack based on the Ancient Magicks spells that share their name.
The Ice nihil signify their special by hissing before freezing you for a short time in a similar way to Ice Blitz, however this can be prevented by using the Anticipation or Freedom abilities. During Fate of the Gods they are also able to freeze you while you're fighting the other Nihil, but when fought after the quest they no longer will.
You can persuade Kuradal to assign Nihil as a task at level 76 Slayer for 50 reward points.