Might be a variation of this (Credit to Prince666) but it now says Spend $20, get free item. Still needs any 2 of the eligible burgers with an order above $20 to activate, but Double Big Mac (Priced around $10) gets you the best value. Must be an error for it to count by itself towards the $20 min spend so be quick before they fix it, may be pre order.
Prices vary by store, so if (un)luckily your store has the Double Big Mac for less than $10 you'll need to add a dollar or so worth of food to pad it over $20
Big mac 🤮
Maybe for a $1 or $2 with the occasional maccas deals is probably what its worth , but quality had really declined lately