Most of the Asterion don't seem very powerful at 1st glance but after seeing Putrify and Love Bites in play I realize that bypassing saves is a huge deal on enemies with legendary resistance, even if the effect is not awesome or persistent.
We were fighting an Ancient Copper Dragon and the Fighter used action surge-attack-putrify to poison the dragon then she used a scroll to cast Summon Undead which attacked and paralyzed the Dragon without a save taking away all its Legendary actions and its flight and letting other players crit on it.
Love bites is not as powerful but makes enemies stop attacking someone in melee and take an AOO if they move, again with no save.
Getting a recharge after a short rest and not requiring either a save or an action to use make these pretty effective against bosses.
We were fighting an Ancient Copper Dragon and the Fighter used action surge-attack-putrify to poison the dragon then she used a scroll to cast Summon Undead which attacked and paralyzed the Dragon without a save taking away all its Legendary actions and its flight and letting other players crit on it.
Love bites is not as powerful but makes enemies stop attacking someone in melee and take an AOO if they move, again with no save.
Getting a recharge after a short rest and not requiring either a save or an action to use make these pretty effective against bosses.
