Counter target activated ability, triggered ability, or legendary spell.
Tale’s End can’t target an activated or triggered mana ability. An activated mana ability is one that adds mana to a player’s mana pool as it resolves, doesn’t have a target, and isn’t a loyalty ability. A triggered mana ability is one that adds mana to a player’s mana pool and triggers on an activated mana ability.
Activated abilities are written in the form “[Cost]: [Effect].” Some keyword abilities (such as equip) are activated abilities and will have colons in their reminder texts, if applicable.
Triggered abilities use the word “when,” “whenever,” or “at.” They’re often written as “[Trigger condition], [effect].” Some keyword abilities are triggered abilities and will have “when,” “whenever,” or “at” in their reminder text.
Abilities that create replacement effects, such as a permanent entering the battlefield tapped or with counters on it, can’t be targeted. Abilities that apply “as [this creature] enters the battlefield” are also replacement effects and can’t be targeted.
If you counter a delayed triggered ability that triggered at the beginning of the “next” occurrence of a specified step or phase, that ability won’t trigger again the following time that step or phase occurs.