I'm pretty new to this wiki, but I have been playing Clash Royale for a while (I'm now in the 3rd arena). This is a well crafted game, and I see that they keep adding new troops to each arena every once in a while. Thus I've decided to share my ideas with you.
Viking (Barbarian Bowl): Similar functionality to the Knight. He runs at a medium speed and has moderate HP, but he hits harder with every hit on a single target (Like an Inferno Tower). 4 Elixir
Wicked Witch (Spell Valley): Flying troop that flies at a high speed (on her broom obviously). Her attacks are rather slow but deal area damage. The drawback is her low HP, barely higher than Minion's. 4 Elixir
Jester (Royal Arena): Has no fighting capabilities whatsoever, but he has a passive aura that covers 4 squares around him which lower the enemy troops attack. If there are no troops around him, he will run away. Very low HP. 3 Elixir
Pirate (Bone PitGood ol' Captain pushing his trusty cannon to wipe the arena of enemy landrubbers. Basically, a Cannon that can move (ranged troop that can't target flying troops). Rather slow, but has a good amount of HP. 5 Elixir
Builder (Builder's Workshop): Stays near building and slowly repairs them (this includes Sparky but exludes Crown Towers). If the player has no buildings he will simply charge at the enemy with his rusty wrench. Won't put up much of a fight due to his overall low stats. 6 Elixir
Troll (Goblin Stadium): Basically, a Giant that can attack enemies with less durability. Nothing much to say here. 6 Elixir
Mind control (P.E.K.K.A.'s Playhouse): Spell that covers a medium arena. Enemy troops in it's radius will attack EVERYTHING in sight. This includes their own allies. 8 Elixir
Goblin King (Goblin Stadium): After he spawns he will pose for 5 seconds after which he'll start attacking and emit a small aura where allies will gain the Rage effect. Similar stats to the Miner. 5 Elixir
Grim Reaper (Bone Pit): Almost identical to P.E.K.K.A. but has barely half of it's HP. However he emits a small aura around him which deals damage over time to everyone around him (This means both enemies and allies). 7 Elixir
And there ya go. I'm open to your critisizm and opinions.