video effects iphone app?

okay so im trying to make a video to upload to youtube. tyler oakley, jenna marbles, danisnotonfire, etc can all add effects to their videos... but im guessing they use a laptop. im using a 3rd generation iphone. price doesnt matter (i have money on my account) and im hoping its not going to be an app that uses up my data plan, but if it does its okay. what i want the app to include: an effect to add text (with preferably different fonts and sizes) on a video, and the ability to add a picture over the video. i hope yall have recommendations! :) and please dont tell me to get a really stupid and cheesy app as a prank. i will check the reviews before i buy it..