What are considered activated abilities?

602.1c An activated ability is the only kind of ability that can be activated. If an object or rule refers to activating an ability without specifying what kind, it must be referring to an activated ability. 602.1d Previously, the action of using an activated ability was referred to on cards as “playing” that ability.

Is ETB A ability?

“Enters the battlefield” refers to putting a permanent onto the battlefield, or to an ability which is triggered when a permanent is put onto the battlefield. It is commonly abbreviated ETB.

Is a Planeswalker loyalty ability an activated ability?

A loyalty ability is an activated ability with a cost of modifying the loyalty counter on a planeswalker card.

What is a mana ability?

A mana ability is an activated ability that creates mana (such as with Llanowar Elves, Birds of Paradise, and Ur-Golem’s Eye), or a triggered ability that triggers off of mana creation and makes more mana itself (such as with Overgrowth or the last ability on Gauntlet of Power).

Do ETB abilities go on the stack?

1) when the creature spell is cast the ETB ability is put on stack immediately ontop of the creature summon spell. 2) when the stack resolves and the creature is summoned to the battle field, then the ETB effect(s) go live.

Can you activate a planeswalker ability in response?

planeswalker abilities act just like any other activated ability. they use the stack and can be responded to, so yes you can doom blade the creature in response to venser’s ability.

Can loyalty abilities be countered?

Yes, it’s correct. The rule you quoted implies that loyalty abilities are activated abilities. And since there is no rule that makes an exception for loyalty abilities, they can be countered like any other activated ability. Remember that countering an activated ability only stops it from resolving.