Grigori is quite possibly insane and can be heard ranting, uttering various disjointed biblical references and laughing maniacally while hunting zombies in Ravenholm. It is unknown if his laughter and religious references are symptoms of insanity or merely aspects of a dark sense of humor; most likely, they are both. Grigori probably has a form of chronic reactive psychosis, which is not a mental disorder in itself, but psychosis brought on by the experience of a severely traumatic or stressful event.
Grigori appears at various points in Ravenholm, generally standing at a high vantage point from which he proceeds to kill the various zombies in the areas below. Zombies seem to prefer to attack the player when given the choice, except during the final sequence leading up to the mine entrance. Because of the limitations of his weapon, he has to reload frequently, so he is vulnerable to the zombies that can reach his position, such as Fast Zombies, in significant numbers or when operating at ground level.
The presence of a survivor in Ravenholm is first revealed with ominous phrases heard quietly near the first propeller trap encountered by Gordon. These phrases sound Biblical, and Gordon finally sees the face of Father Grigori well after he has battled through several groups of zombies and headcrabs. Above a flaming mound of zombie corpses, Grigori greets Gordon, telling him that he is free to use his traps, but to be careful not to fall into them himself. He later shoots a Fast Headcrab that was about to attack Gordon from behind and advises him to be vigilant in Ravenholm. Later, he also throws Gordon a SPAS-12 shotgun, giving him the advice to "Aim for the head".
When Gordon finally meets Grigori on-foot, it is near the church mentioned earlier by Grigori. From atop a roof, Grigori can be seen below, telling Gordon that he is moving a tram to the rooftop to allow him to come down. After Gordon has gotten into the tram and is face to face with Grigori, he informs him that they will have to travel through the graveyard to reach the mines. He tells Gordon to "tread lightly", as the graveyard is "hallowed ground." Grigori then accompanies Gordon through the graveyard, helping him to fight off the zombies before allowing him to escape into the mines.
Grigori's eventual fate is left ambiguous; once he has opened up the gate at the graveyard, Gordon is free to go, with Grigori telling him to "look to his own salvation" before then laughing in a crazed manner. If the player remains at the gate after having been "escorted" to the mines, Grigori continues shooting at zombies, and tells Freeman to "Get going," and that "No one wants to stay in Ravenholm." Eventually, Grigori will detonate some nearby fuel tanks as zombies break out of a crypt; he runs through the flames laughing and firing before taking cover in the crypt entrance and continues killing zombies for some time, then disappears inside.
Given the circumstances of his last encounter, even if he survived the large zombie horde that he and Gordon stirred up, the destruction of the Citadel could have obliterated Ravenholm. The time and distances involved are sketchy, but as Gordon manages to reach Black Mesa East in about 2 to 3 hours or so, and Ravenholm is just outside Black Mesa East, it can be judged that Ravenholm is around 20–40 km from City 17. Seeing as the forests outside City 17 are relatively untouched, it can be reasoned that Grigori escaped the Citadel explosion. It is not impossible that he escaped by waiting out the fire and running away, but being slightly insane, he may have fought to the end anyway. In Raising the Bar, they say his eventual fate was left up to the players to decide and that they did not plan to re-use the character in the series.