If a continuous effect sets a creature's power to a specific number, does a subsequent +1/+1 counter still apply?

Magic resolves continuous effects that modify power and toughness through a strict layering system defined in CR 613. Effects that set a characteristic to a specific number (e.g., "This creature's power is 2") apply in layer 7b. Effects from counters (like +1/+1 counters) apply in layer 7c. Because layer 7c comes after 7b, the counter's bonus is always added on top of whatever the set value is.

This is true regardless of the timestamp of the setting effect. Even if the power-setting effect was applied after the counter was placed on the creature, the counter still applies in layer 7c. Timestamp order only matters when two effects operate in the same layer (CR 613.7).

It also does not matter whether the counter was placed before or after the power-setting effect became active. Counters are a physical state of the object and are always evaluated at layer 7c (CR 613.7c).

Example: Your 2/2 Bear has a +1/+1 counter on it, making it effectively 3/3. Your opponent enchants it with Livewire Lash's effect, or suppose an effect sets its power to 1 (layer 7b). The resulting power is 1 (from the set effect) + 1 (from the counter at layer 7c) = 2. The counter still contributes its +1.

Relevant rules: CR 613.3 (the layer system), CR 613.7b (characteristic-setting effects), CR 613.7c (counter-based modifications).