Lil' Zik is a pet that can be obtained from completing the Theatre of Blood. It is a much smaller version of Verzik Vitur's final form. Players have a chance of receiving the pet when looting the monumental chests in Verzik's treasure vault.
When a player receives the pet, it will automatically try to appear as their follower. At the same time, a red message in the chatbox will state You have a funny feeling like you're being followed.
However, if a player receives a pet while having a follower out (for example, a cat), it will be placed into their inventory. When this occurs, the message in the chatbox will instead state You feel something weird sneaking into your backpack. If a players inventory is full and they have a follower already, they will not receive the pet.
On death, if a player loses their pet (as a follower or in your inventory) it will wander around for 30 seconds before disappearing completely.
Players can pay a one-time fee of 500,000 coins to Probita in East Ardougne to have this pet insured. Should the pet be lost while insured, it can be reclaimed for 1,000,000 coins.
The drop rate is dependent on the player's performance in the raid, unaffected by that of teammates, ranging from 1/650 to 1/6,500. The maximum rate is reached with 10 individual points (which are invisible to the players; the maximum per player is 32, or 18 if not including the MVP bonuses for each room). The highest rate is reached by dying no more than twice per raid, with more deaths allowed if the player deals the most damage in some rooms, assuming participation in each room.
For an exhaustive list of all known sources for this item, see here