Frennning allows you to create cards with very high stats and powerful synergistic effects not otherwise available, but it comes with the cost of investing all its constituent cards into one place (zone/type), meaning if it is removed, you loose everything you invested into it. it is the risk/reward trade off of the Fren mechanic.

almost all card have a base stat of 4, which is its combined effect power (number of uses), health (mtg toughness), and attack