There isn't any good direct comparison to Mangara's abilities, but the closest thing that popped into my head is Runic Armasaur, another creature whose card drawing ability is entirely dependent on your opponents' actions, making the card inconsistent where it sometimes draws you zero cards and sometimes floods you with card draw
Example Here is an example deck that I played on Arena with some friends from my local game store
The Gitrog Monster is a maker of majestic vistas
Nogi, Draco-Zealot discounts your Dragon spells, and if you control three or more Dragons, Nogi gets to turn into a Dragon and fly alongside them
Includes Atraxa
So, maybe you have five decks you absolutely adore, but then you have five more deckboxes that have other decks in for 6-12 months (maybe more, maybe less) before you deconstruct them to try something else