The rest of the Collector's 'attacks' comes from his cohorts.

Suffice to say, Lifesteal is his worst attack just by merit of making the fight longer.

Comparatively, Life Steal has a high damage range, high crit rate, can bleed and mark the victim, and worse off heal the Collector for 10 HP.

His most used attack is Show Collection, which hits your front two ranks for ~10 stress damage, but does nothing else so its something you hope for. His other attacks can range in threat value depending on the situation. Collector will open up the fight with this skill, and will use this skill in elevated frequency as you kill more of his summons. Said attack, known as Collect Call, will summon three heads in varying amounts from the classes that you pick up heads from in secret rooms. Based on the Yellow King, this midboss is primarily a summoner and will more than often spend time refreshing his minions should he ever find himself in short company. The Collector is a midboss seen randomly in the dungeon, and is set to appear once you have more than half your inventory full. If anyone finds a source I will credit them) The Collector

Darkest dungeon collector meme