This commander night; phyrexian mana has infiltrated curiosity to the extreme. Allowing you to cast spells that cost 5 or more for up to 2 less at the cost of life, on the flip side, all spells that cost 4 or less cost 2 more (or 4 life more). It is important to remember this only effects colorless mana.
Utilizing the new Defiler cards from Dominaria will go a long way to capitalize on this effect lowering your mana cost even more.
This effect goes a long way to make big mana cost cards far more playable, and smaller mana cost cards more difficult to play, keep this in mind when bringing your deck in this Saturday. That counterspell costs 2 blue plus 2 phyrexian mana, that free Fierce Guardianship costs a minimum of 2 phyrexian mana even when "cast for free", Sol Ring costs 1 and 2 phyrexian mana, and so on and so on.