MythicMobs

When MythicMobs is installed, three extra triggers become available. Detection is automatic — no config needed, just have MythicMobs enabled when the server starts.

Trigger	Counts when the player...	Progress
kill_mythic_mob	kills a MythicMob	1 per kill
damage_mythic_mob	damages a MythicMob	the damage dealt
signal_mythic_mob	receives a signal from a mob's skill	1 per signal

kill_mythic_mob

The target is the mob's internal name — the top-level key from your MythicMobs mob file, not its display name:

objectives:
  slay_boss:
    name: "&#FF6B6B&lDragon Slayer"
    trigger: kill_mythic_mob
    target: SkeletalDragon
    required: 1

damage_mythic_mob

Progress is the damage dealt, so required is a total damage amount, not a hit count. Use the internal name as target, or any to count damage against every MythicMob:

objectives:
  wear_down:
    name: "&#FF9A8B&lSiege Participant"
    trigger: damage_mythic_mob
    target: SkeletalDragon
    required: 500

This is great for boss events — every participant can complete the objective, not just whoever lands the killing blow.

signal_mythic_mob

The most flexible of the three: the objective progresses when a MythicMobs skill sends a signal to the player. The target is the signal name, and it's required — there's no any.

In your MythicMobs skill config:

Skills:
  - signal{s=BOSS_PHASE2} @PIR{r=30}

And in the quest:

objectives:
  witness_phase2:
    name: "&#D3DBE3&lSurvived the Frenzy"
    trigger: signal_mythic_mob
    target: BOSS_PHASE2
    required: 1

Since signals can be fired from any point of a mob's skill tree (phase changes, mechanics dodged, timed events), this lets quests react to basically anything that happens in a boss fight.