Then you can sacrifice the creature when you activate mana abilities just before paying the cost
As a sorcery, you may pay the mana cost of a locked door to unlock it.) Two or more objects (cards, permanents, spells, etc.) have the same name if they have at least one name in common, even if one or more of those objects have additional names
If you have a way to also discount your red spells, Birgi helps you even generate excess mana to potentially cast your whole deck
For example, if you want a Rush Deck to flood the battlefield with low level creatures, you will probably want less 5 Cost Cards and more 2 or 3
Then you can cast mana ramp outsize of Green
Im sure this otter artificer helps some sort of massive token combo deck win a turn faster, which isnt nothing, but I continue to find better cards than this to slot into my decks