In Challenge Mode, Gregorovic gains increased combat stats. His life points, however, still remain at 200,000, unlike the other generals who are given an additional 100,000; however, his healing ability is likely able to heal him around this much.
Gregorovic's abilities are somewhat altered compared to normal mode, and he also has a unique ability when he first falls to 0 life points.
- His "RISE, CHILD!" will summon two spirits instead of one. In addition, these spirits have a faster movement speed compared to those in normal mode.
- Gregorovic's shadows are summoned at 140,000 and 60,000 life points, the same intervals as in normal mode. However, an additional shadow copy is added to them.
- When Gregorovic first reaches 0 life points, he will turn the player into a shadow copy of himself while he starts healing himself with an initial set of 5,000 before healing for 10,000 afterwards every few ticks. The player will need to kill six Wight Hunters through auto-attacks (abilities cannot be used). In addition, only food and saradomin brews will be capable of healing the player.
Players should fight Gregorovic just like in normal mode, as he still follows the same attack pattern. However, use of Soul Split is completely discouraged in hard mode, as Gregorovic's attacks deal far more damage at an increased accuracy rate which makes it near impossible to recover lost health from it alone.
Begin the fight in one of the corners, preferably the north-western corner so Gregorovic will only summon mania and delirium spirits. You do not want to have a spirit of rage touch Gregorovic which will make the fight even more tedious. As soon as the spirits spawn, immediately attack the mania spirit, as spirits in hard mode "run" towards Gregorovic and relying on Ricochet or Chain alone to get their attention is extremely unreliable.
Once Gregorovic falls to 0 health, he will turn the player into a shadow copy of himself. He will immediately heal for 5,000 life points, before healing for chunks of 10,000 at a time. Several Wight Hunters will spawn and attack the player, using magic, ranged or melee depending on their combat style. The player will only be able to attack with auto-attacks. Lure all the attacking hunters close to each other, as your auto-attacks will bounce onto nearby targets. Players will always hit the wight hunters for 2,000-4,000 damage. Make sure that your health is high before Gregorovic falls at 0 health, as eating during in shadow form will delay your attacks and allow Gregorovic to sneak in extra heals.
Once six Wight Hunters are killed, Gregorovic stops healing and says "No! Allow yourself to be consumed!" and the player is returned to their normal form. Gregorovic does not restart his attack pattern; instead, he will start from where he left off prior to falling at 0 health at the time. Note that Gregorovic will recreate four shadow copies of himself if he healed up to 60,000 or higher before the player killed six Wight Hunters.