Made it to Arena 7 (Royale) as a F2P player. Feels good, man. I fully expect to be knocked back down soon, but I'm actually experiencing decent success so far - have three A7 chests to open.
Deck:
Goblin Hut (L5)
Barb Hut (L5)
Barbarians (L8)
Wizard (L5)
Musketeer (L5)
Mini Pekka (L5)
Arrows (L7)
Prince (L2)
Generally open with one or both of the huts. The 4 barbs are used on defense to shut down hog rider, PEKKA, Musketeer, etc. Mini Pekka is fucking INCREDIBLE on offense if you can sneak him into range behind other units, but he's often used on defense as well, placed to take out an opponent's Wizard or other high-value target, or sacrificed to take out a defense structure.
Deck is very high mana cost and usually loses to people doing things like tossing goblins to one side of the map then placing prince on the other side - I usually don't have a chance to respond to both.
Most common win condition for me is to place both huts on one side, and almost all players, even at high levels, over-commit to defense. If they place 2x units in defense, I usually drop barbs/pekka/prince + wizard on the other side and burn down the open tower. If they clean up the barb/goblin attack more intelligently, or get too aggressive for my deck to get going, I usually lose.
Took me 246 total wins to get here.