For every lore thats lost, you get to draw a card into your hand
The ooze itself in the artwork appears to be eating a pig, and the effect of destroying a permanent and gaining stats equal to the total CMC of the permanent it "eats"
You can pay 800 life points to negate the activation of a Spell or Trap card on the field and destroy it
Given how much the Pokemon TCG has, appropriately, evolved over the last few decades, you wont find these being used in decks in the present day, but of course thats generally not why fans get hold of them
The incredible variety of valuable Pikachu cards is just one example of what happens when you combine the passion of the Pokemon fandom with the desirability of the TCG
The only other information offered up for now, other than the promotion seemingly being exclusive to McDonald's in the UK, is that it will begin on August 3, 2022