If it is a Crack one-shot?
Make Harry succeed half way. A Group of people he had strong bounds to(of friendship, love, rivalry and ect.) - about 20--40 people, get the memories up to the time of the Ritual or their death. The thing is that Little Harry in the past gets all their combined magical power added to his own, instantly catapulting him to OVER 9000 levels(Flamels, Voldemort and Dumbledore are among loopers). Then crack begins.
Loopers begin to do what loopers usually do - plot. With 30 Xanatos Pileup of spectacular proportions being the result. Remember - for all their memories, they are as powerful as they were in canon at this point of timeline. So only about 5--10 of them (adults) can begin to actively change things. The rest are in desperate need for some Training From Hell. And most of them(at least in the beginning) think that they are alone back in time(The idea that someone can be back with them too did not even as much as cross the minds of more then half of them). And every single one has Harry as centerpiece of their plans.
A problem. Harry has more magical juice then Negi Springfield(circa chapter 300 of manga). With Lily's protective magic finally getting enough power(and then some...20 times over some) he is harder to injure then Jack Rakan and regenerates faster then Inugami Kotaro. He also has devil's own luck.
He has just found out that he is free from Dursleys(and has yet to be told otherwise). Harry certainly has no desire to be trapped again. Magic reacts. Hilarity Ensues.
p.s. Consider that for all his ignorance, his Wingardium Leviosa can launch stones into LEO, his Protego can tank low-yield nukes and that his body is rapidly getting a decent Magic Knight-grade enchantment. :evil2:
