It won't trigger again while the ability is on the stack, but if the ability is countered and Dark Depths is still on the battlefield with no ice counters on it, it will trigger again immediately
14 Kelsien, The Plague Starting off as a 3/3 Assassin, Kelsien, the Plague gets +1/+1 for each experience counter you have
Where Zombies starts to differ from Vampires is in the number of lords
If you squint, its like an extra copy of Syr Konrad, the Grim
While only OK against aggro decks the card has proven incredibly good against midrange, control and combo decks too
Murmuring Bosk, for example, pairs nicely with fetch lands that look for a Forest, while Tournament Grounds is perfect in decks heavily centered on Knights