Exiling things from graveyards is something you just want to do in Magic, as it can often disrupt your opponents gameplan
If you discard a card with madness to pay the cost of a spell or activated ability, that card's madness triggered ability will resolve before the spell or ability the discard paid for
A mid-tier set that introduces Regice, Registeel, and Regirock , plus ancient-themed Trainers like Ancient Tomb
In games of Commander, the only question regarding Portal to Phyrexia is just how you plan on getting it into play
Lets say you cast Summoner's Pact, then each of your opponents copies Summoner's Pact thanks to Hive Minds triggered ability
The joke for a while has been that every supplemental set is just meant to add cards to Commander, but this set is explicitly meant to do exactly that