There was a strong debate in this thread about the interaction between the cascade ability and the card Bond of Agony. It appears that it works thanks to this part of the comprehensive rule:
G24.1 - X

G24a - If a cost has an "{X}" in it, the value of X must be announced as part of playing the spell or ability. (See Rule 409, "Playing Spells and Activated Abilities.") While the spell or ability is on the stack, the {X} in its mana cost equals the amount announced as part of playing the spell or ability. If a card in any other zone has {X} in its mana cost, the amount is treated as 0. If you're playing a spell that has {X} in its mana cost and an effect lets you play it without paying any cost that includes X, the only legal choice for X is 0. This does not apply to effects that only reduce a cost, even if they reduce it to zero. See Rule 409, "Playing Spells and Activated Abilities." [CompRules 2005/10/01]

G24.1b - In triggered abilities, X is defined when the ability resolves. It may be defined by the text of the ability, by a keyword ability of the card, or by the trigger event. See Rule 410, "Handling Triggered Abilities." [CompRules 2003/07/01]

G24.1c - In other cases, X is defined by the text of a spell or ability. If X isn't defined, the controller of the spell or ability chooses the value of X. All Xs on an object have the same value.
This is quite clear that the Bond of Agony cost is not reduced to nothing (since one has to pay X life). So it's quite clear that X can be something else than 0.

However some people (including level 2 judges???) still consider that it might not work. I don't get why.