Tanjis attacks persistently (although less so than the other two deepling guardians): he will focus on the same target for many turns. Tanjis will typically (but not always(?)) target the first non-knight player to hit him after being encountered/challenged, and like other monsters he will change targets when they are out of range or when he can no longer shoot them. Unlike most other monsters however (or somewhat like Deepling Guards) he will not change targets to a character in his path.
Tanjis, Expeditus Profundis, is one of the three depth lords. He is the most harmless but most frequently appearing of the deepling guardians. Access to his lair is earned by helping to repair the ramp to the Ancestral Grounds, during the Liquid Black Quest. Teams may enter each guardian's lair once for each time they make a sufficient attempt to repair the ramp to the Ancestral Grounds. However, access to any further guardians is revoked if players open any treasure chest outside of their lairs.
Tanjis spawns each 3-10 minutes depending on players online, and cannot be blocked from spawning (same as the inquisition bosses, pharaohs and the black knight). Teams can stay in Tanjis' room for 20 minutes, the timer starting when they enter the teleport. Reentry is denied after players gain experience from Tanjis. Thus, teams can earn a few minutes by jumping out and in Tanjis' lair when the first Tanjis is on his last hitpoints.
You will need a lot of firepower, perhaps 4 or more players of level 150+. It's highly recommended all team members use Bronze Amulets due to his retargeting behavior. The general strategy is to trap Tanjis and fire at him until he is dead.
Trapping Tanjis can be difficult. Because of his retargeting behavior, the shooters are advised to stand away from Tanjis while the blocker lures and traps him. The environment makes trapping him difficult also, knights will almost always be forced to stand in waves/beams because Wild Growth will not last long enough.
Once trapped, it's a battle against his healing.
Tanjis will attack shooters very frequently, even when trapped. Shooters can expect to be hit with strong Mana Drain and Ice-based attacks every 2-5 turns. Shooters are recommended to position themselves away from other team members, or move to another location when they find themselves being targeted (but be mindful of his waves). This avoids unnecessary mana/health loss for the other members.