Tawnos, Urza's Apprentice

Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keyword abilities (such as equip) are activated abilities and will have colons in their reminder text. An activated mana ability is one that produces mana as it resolves, not one that costs mana to activate.

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 the beginning of" in their reminder text.

Tawnos's ability targets an ability that is on the stack and creates another instance of that ability on the stack. It doesn't cause any object to gain an ability.

An "artifact source" is a permanent, spell, or card in any zone with the card type "artifact." For example, Tawnos's ability can target a cycling ability you've activated if the discarded card is an artifact card.

The source of the copy is the same as the source of the original ability.

If the ability is modal (that is, if it says, "Choose one —" or similar), the mode is copied and can't be changed.

If the ability divides damage or distributes counters among a number of targets (for example, the ability of Verdurous Gearhulk), the division and number of targets can't be changed. If you choose new targets, you must choose the same number of targets.

If the activated ability's cost contains a choice, such as a creature to sacrifice or a number of counters to remove, the copy uses that same information. You can't pay the cost again, even if you want to.

Any choices made when the ability resolves won't have been made yet when it's copied. Any such choices will be made separately when the copy resolves. If a triggered ability asks you to pay a cost (such as that of Mirrorworks), you pay that cost for the copy separately.

If an ability is linked to a second ability, copies of that ability are also linked to that second ability. If the second ability refers to "the exiled card," it refers to all cards exiled by the ability and the copy. For example, if Tidehollow Sculler's enters-the-battlefield ability is copied and two cards are exiled, they both return when Tidehollow Sculler leaves the battlefield.

In some cases involving linked abilities, an ability requires information about "the exiled card." When this happens, the ability gets multiple answers. If these answers are being used to determine the value of a variable, the sum is used. For example, if Soul Foundry's enters-the-battlefield ability is copied, two cards are exiled. The value of X in the activation cost of Soul Foundry's other ability is the sum of the two cards' mana values. As the ability resolves, you create a token copy of each card.