Countering a "When Cast" Ability

Question

If an opponent casts a spell that has an "when cast" ability, e.g. the cascade from Bloodbraid Elf, can I counter that ability - I think it'd be a "triggered" ability - using a card like Tale's End?

Answer 1

Yes, you can. An abilities that triggers when casting a spell is a triggered ability. Thus it can be countered by anything that counters triggered abilities such as Tale's End.

Answer 2

All abilities that begin with "when", "whenever", or "at" are triggered abilities:

603.1. Triggered abilities have a trigger condition and an effect. They are written as “[When/Whenever/At] [trigger condition or event], [effect]. [Instructions (if any).]”

In the case of abilities such as cascade, the reminder text on the card shows that it starts with "when", but note that reminder text is not the actual rules, it's just a summary. To show for certain that Cascade is a triggered ability, you have to look at the rules entry for Cascade itself:

702.85a Cascade is a triggered ability that functions only while the spell with cascade is on the stack.

Same for other abilities such as Ripple. But the reminder text isn't going to have "when" unless the real rules actually have "when".