For more info on the lore, you can take a look at the trailer video below, shared via the official Lorcana website
When it enters the battlefield or when it attacks, you can either add or remove charge counters from Immard, helping keep it alive by giving it indestructible or dealing four damage to any target
it basically renders weighing worthless and guarantees you get a fair chance of pulling rare cards
Here are some of the most valuable cards in the Obsidian Flames expansion based on market prices from TCG Player at the time of writing: Tera Charizard ex (Special Illustration Rare) $162 Buy from TCGPlayer Tera Charizard ex (Hyper Rare) $76 Buy from TCGPlayer Tera Charizard ex (Ultra Rare) $48 Buy from TCGPlayer Geeta (Special Illustration Rare) $30 Buy from TCGPlayer Tera Charizard ex $25 Buy from TCGPlayer Pidgeot ex (Special Illustration Rare) $20 Buy from TCGPlayer Revavroom ex (Special Illustration Rare) $20 Buy from TCGPlayer Ninetales (Illustration Rare) $19 Buy from TCGPlayer Tyranitar ex (Ultra Rare) $18 Buy from TCGPlayer Poppy (Special Illustration Rare) $15 Buy from TCGPlayer Because the Obsidian Flames expansion is fresh on the market, its likely that these values will fluctuate heavily over time
The reasoning is that they are worth two points, so losing one quickly turns the tide in favour of your opponent
Notably, casting a multicolor card will trigger two or more of these abilities, making Aragorn more efficient and rewarding for players using him in a color-heavy deck with lots of multicolor cards -- of which Tales of Middle-Earth has plenty
