Board Thread:Theories and Speculation/@comment-2165692-20170426120148/@comment-734582-20170426145821

BerserkerPhantom wrote: Then he wouldn't have summoned a snake. He wouldn't have summoned anything. That's a huge speculation that he did it off-screen and somehow screwed it up because "LOLZ, WHY NOT HUH? When in the Ninja Tools Preparation Room, boruto says "i'll just use my Summoning Jutsu. There are some scrolls in this room right?

This heavily implies that he made his own contract. We don't know how powerful or sentient that chimera is, but we've seen from Madara that the contract can be tampered with and we've seen from Edo Tensei that as long as you have the information, anything can be summoned, even spirits from the afterlife.

This leaves the most likely possibility: Boruto screwed up the contract, which opened a way for the Chimera to come out. Judging by it's aura in an earlier episode, it seems the connection is the dark chakra.

Like i said, Jiraiya's explanation tells us nothing about how the contract is formed or how complex it even is to make one. Boruto possessed the scroll for a while and is clearly close to Konohameru so he probably had a chance to look inside. That means he had a chance to copy the formula. (he was smart enough to know the seals despite not using the seals or blood in his first attempt so he clearly did his homework).