More theories... good good. Although nobody seems to have picked up on one of my last hints.
Guess I can throw another bone on the pile, but this is the last!
There is a very high possibility of me speculating just the finest bullshit here. But if not, I guess you're talking about the condition that Greg mentioned at the end of ep19, saying that if any inheritor share his/her conditions with other beneficiary then their rights over the inheritance become null and void. Later, in ep22 if you invite Bella to the BH she tells MC that Elaine told her explicitly about her conditions, in addition to MC's conditions, the latter a bait which MC buys and says "yea correct", which worries me that it can be considered as the MC accusing his own conditions and therefore at risk of losing everything (if Bella is the third one, and specially if she's the viper). But on this last point, it would make no sense that Cheeky wants MC to blow away his money so easily (should have at least given the option to choose actions and the yellow "big decision" warning) so maybe this was not big deal. Or maybe it really is, and part of the plot soon to come is an adventure of its own to reverse this dumb move.
Anyway, if I understood this correctly, then there are two options:
a) Elaine is the one aware of the conditions from the start, thus the cheater, but if according to Greg the sub-clause was not to reveal her conditions then she practically gave up every and each right of hers over the inheritance consciously, which not only is in detriment of her own interests, but also contradicts the story told by Bella who mentions a lot of treacherous actions which would have no logic (also controverting how Greg and the fortune teller depicted this "third" person, i.e. the "viper"). Unless, remembering Greg's words, this condition was put upon *some* of the beneficiaries, not mentioning whom specifically, so maybe Donald excluded Elaine from the sub-clause, hence she can comfortably speak about it. But even then, as the bomb dropped by Ace says, if the conditions put upon Elaine were vindictive, then it's very unlikely to let her speak so freely about her conditions, something that she was always reluctant to do precisely because of the clauses (if not for other hidden reason). So that leaves us with a second option which is:
b) Bella just made up this story mentioning the conditions of everyone else, practically revealing herself as the one who knew all the conditions beforehand, thus confirming she's definitely the viper.
If this analysis is correct and we do Occam's Razor then the identity of the viper is evident.