I will post some in-game options here, please excuse if you have already tried these:
Start Dungeon Quest
Press the Options button on the main menu
Press "All Damage Numbers" to turn off all of them showing, or to only show crit damage numbers
Turn off "Show enemy HP Bars"
Turn off "Show ally HP bars"
Screen Shake:On should be set to "Screen Shake: Off"
High FX button should be set to "Low FX"
Medium Shadows button should be set to "NO Shadows".
This will turn off all possible "extra effects" in the game.
If at all possible avoid getting huge groups (20+) of enemies together and attacking/defeating them all at once. This can cause very bad FPS for your device.