The boss shields himself, you need a champ with buff removing or buff stealing ability here. I think the magic keep is by far the hardest of all keeps. 

Here is a list of champions with the needed ability. If you don't have one of them now, a Skinner could help out until you get something better. You can find Skinner in the sewers in campaign.

You  can  break  through  the  first  shield,  but  the  second  shield  and  increase  defense  on  his  A2  make  the  runs  longer.  You  could  use  remove/steal  buffs,  or  if  not  just  use  damage  and  turn  meter  control.

Also,  in  my  opinion,  Spirit  Keep  is  the  hardest  (or  most  annoying)  for  me,  while  I'd  think  Force  Keep  would  be  the  hardest  early  game,  due  to  his  high  defense  and  starter  champions  are  magic  affinity.

it's a her

It's a her.

Wow, the gender of the magic keep boss is important enough to make 2 posts in a weeks old thread. 👏

How do you know it's a "her"? Maybe the magic keep boss identifies himself as a male.

I know I wondered the gender then aumlove said it was female and to think of it, it makes perfect sense. void and force males, so it would make sense for magic keep to be female, to be 2-2. Magic keep does have very long hair if you look closely. The twirling she does is while she sheilds only seen in female champions.

Game changing news! 😁