As far as Lila was concerned, all courtesy should be common.

Lila, Hospitality Hostess

You may look at the top card of your library any time.
You may cast common spells from the top of your library.
Guests you control get +1/+1.

Unfinity

Common cards have black expansion symbols. Cards from before Exodus™ don’t have expansion symbols; their rarities can be found on their Gatherer entries. (Cards with the land rarity, including basic lands, also have black expansion symbols, but Lila doesn’t let you play lands, so this hardly seems worth mentioning. Oh, sorry.)

Lila’s middle ability doesn’t change when you may cast those spells. You still pay all costs for those spells as well.