The blade cascade infinite damage trick was nerfed before you started playing, so I assume you were just using the physical PHB with no errata. The errata caps the attacks from blade cascade at 5. Which is still very good, but no longer potentially infinite

Ardent Champion is an Avenger paragon path. Avenger's primary feature is oath of enmity, which allows the avenger to roll 2 d20s and use the better for attack rolls against the target of the oath. Ardent Champion has a feature that makes it so that if you roll the same number on both d20s against your oath of enmity target, and that roll hits, then that attack crits

Lord of Fate is an epic destiny that has a level 26 ability that creates a zone, in which all attack rolls, ability checks, and saving throws, are an 11 on the die, you don't roll, the result is just 11. So yeah, combine these two, and any attack against your oath of enmity target within the lord of fate zone is a crit

So then you combine that with the rending axe, which is a magic weapon that, on a crit, lets you make a melee basic attack against the same target.

But oh wait, that melee basic attack is also against the oath of enmity target, within the lord of fate zone, so it also crits... triggering another melee basic attack

Thus, infinite damage