If you have 7 "Crystal Beast" cards with different names on the field or in your Graveyard: Special Summon 1 "Rainbow Dragon" or "Rainbow Dark Dragon" from your Deck or Graveyard, ignoring the Summoning conditions.
These are the only Crystal Beast monsters and they also total only 7 different names, meaning that if you want to use Rainbow Gravity you would need to add at least one copy of each of these Crystal Beasts to your deck.
You could use That Grass Looks Greener in a 30 card deck to try and mill out all the necessary Crystal Beast monsters to fulfill Raibow Gravity's activation condition. To take this further you can use the skill Meet My Family to create a 38 card deck, milling more cards with That Grass Looks Greener.
I don't know what's wrong with the "still in deck" one, but sending the dragon to the graveyard with Jesse's skill never gonna work in the first place since Rainbow Dragon is never summoned properly, meaning Rainbow Gravity can't revive it.
Which is something that has been mentioned MULTIPLE TIMES in this comment section.
Semi-Nomi rule basically states that a monster that can only be special summoned must first be special summoned properly (by the listed effect) before it can be summoned from the graveyard/banished zone.
TL;DR, summon Rainbow Dragon properly first.
You cannot use this card to complete the mission of summoning rainbow dragon, i've tested it
Ignoring summoning condition just means you can revive a monster that normally cannot be revived.
However, ignoring summoning condition also means it is not a proper summon, therefore the monster must be properly summoned first (using the way written on the monster's text) before it can be revived.
Hey if they do give us this eventually its cool if they don't whatever