Much like Rabble Rousing seems made for Isshin, Reservoir Kraken seems like it exists to enable Ninjutsu decks
Because it says up to one target creature in the Enrage trigger, you are able to stop this ability whenever you want, so you can save the Altisaur to fight again later, or if need be, you can have it fight to its death to take out problematic creatures
Creatures can still attack you while you have protection from everything, although combat damage that they would deal to you will be prevented
All of the Nazgl are seen mounted on their horses
This Story Spotlight features a captive Pia Nalaar being forced to fight against the Inventors' Fair Head Judge Tezzeret, who is secretly a Planeswalker native to the Alaran Shard of Esper and an agent for various malignant forces such as New Phyrexia and Nicol Bolas
So if trying something like Rona + Unctus could see that being a good fit in a Leyline build