I've been playing in the Coliseum since I started walking an hour each day to entertain myself and make some dragon cash as well. Since I wanted to also start exalting dragons, I created a controller set up via JoyToKey geared toward Mire Millionaire dragons. I use a Switch USB controller and this is my set up (can be translated to different controller types):
Left mouse stick: move the mouse
ZL/ZR: Left click
L/R: Escape (optional)
Y (left): A, Q
B (bottom): D
A (right): E
X (top): W, F
- button or whatever your heart desires: F5 (reload for bosses)
Building breath for battle:
Left, right (meditate)
Left, top, left (haste)
Left, bottom, left (rally)
Bottom OR left, bottom, left (defend OR rally; depends on if meditate or scratch pack)
Attack enemies in a three pack:
Left, left, left
Left, left, top
Left, left, right
Attack the top left/extra enemy in a four pack:
Left, left, bottom
Heal:
I just use the left stick and ZR/ZL to click a potion then my Mire Millionare
Accidentally pressed an attack button when you want to heal? Use L/R to back out or just use the left stick to click out.
Hold down your left click mapping on a dragon to drag them in/out of the coliseum team. I personally moved my exalt tab to the front of my lair temporarily to make it easier to switch fodder in and out.
Hope this helps someone else. Feel free to adapt as needed; this is what makes the most sense to my brain personally.
And a screenshot of how the buttons are set up for visual purposes:
