Do look at the pvp section of this forum, there’s a lot of strategy advice & tips for pvp there.
I won’t tell you the 15 arks that you should be taking, best way is for you to play around with them & see which one works the best.
I wouldn’t take frillzeon unless I have 3 fire arks together. Do you have goldenhorn? It’s a great ark, it has guardian & last will, great to put together with frilzl & magma.
In master, I doubt anyone doesn’t know about the raioh angelon DP combo, about its showdown, I dare to say that you will be lucky if you could use it 1 out of 10 matches. If I am right with this one, I would suggest you to not even bother taking DP, bring typhonwyrm, move your wyrms even more to the back, put halopard in between 2 of them & raioh in between the other 2 of them.
What OM & other egg exclusives do you have?
What have been your main challenges in master league?