606. Loyalty Abilities
606.1. Some activated abilities are loyalty abilities, which are subject to special rules.
606.2. An activated ability with a loyalty symbol in its cost is a loyalty ability. Normally, only planeswalkers have loyalty abilities.
606.3. A player may activate a loyalty ability of a permanent they control any time they have priority and the stack is empty during a main phase of their turn, but only if no player has previously activated a loyalty ability of that permanent that turn.
606.4. The cost to activate a loyalty ability of a permanent is to put on or remove from that permanent a certain number of loyalty counters, as shown by the loyalty symbol in the ability’s cost. This cost may be modified by other effects. 606.5 If the total cost to activate a loyalty ability contains multiple costs to add or remove loyalty counters, those costs are combined into a single cost to add or remove loyalty counters, as appropriate.
Example: A player controls Carth the Lion, which says, in part, “Planeswalkers’ loyalty abilities you control cost an additional [+1] to activate. That player also controls a planeswalker with three loyalty counters. To activate one of that planeswalker’s abilities that normally costs [+1], they put two loyalty counters on it. To activate one of its abilities that normally costs [?4], they remove three loyalty counters from it.
606.6. A loyalty ability with a negative loyalty cost, taking into account any additional costs, can’t be activated unless the permanent has at least that many loyalty counters on it.