Flying, lifelink for a double life swing, and then vigilance to hold back and deathtouch to trade up, pretty minor here
Suddenly your 4/4 is a 6/6 that gives all of your permanents hexproof - which is absurd on its own - and then also puts two +1/+1 counters on each of your creatures at the beginning of combat on your turn
This Guildmage makes your army a nightmware to block, and it ensures those that double block have a higher chance to eating the dust as well
Finally, you can mitigate the damage you take as it comes via creatures like Souls Attendant or Essence Warden, or gain a bunch of life through cards like Exsanguinate and Debt to the Deathless to offset early losses
To show how efficient this card is for the right deck, the final versions of Miracle Grow, which were dubbed Super Grow, used Mystic Enforcer as a finisher, since by the time you'd get around to casting it you had an all but guaranteed 6/6 flyer for four mana