The latest update to the game adds what the developers are calling "Ultra Quality" graphics. This is for the iPhone 6s, iPhone 6s Plus, iPad Mini 4, iPod touch 6, and iPad Pro.
It also unlocks screen flip for the iPhone 6 Plus, improves shadow quality on iPhone 6s, and fixes a world map bug on 6s and 6s Plus.
Finally, some of the enemies have been tweaked and the controls have apparently been improved.
The 2.6 update with all this included is available to anyone who owns the game right now.
And if you don't own it then you can purchase it for £6.99 / $8.99 on the App Store.