Does Humility override a layer-7 effect that gives a creature a power and toughness boost?

Power and toughness modification happens in Layer 7, which is divided into sublayers: 7a (characteristic-defining abilities like Tarmogoyf), 7b (effects that set P/T to a specific value, like Humility), 7c (effects that modify P/T by a specific amount, like Giant Growth), and 7d (+1/+1 and -1/-1 counters), and 7e (effects that switch P/T).

Humility sets all creatures' power and toughness to 1/1, which applies in sublayer 7b. Effects that boost a creature's P/T — such as 'gets +2/+2 until end of turn' from a spell like Giant Growth — apply in sublayer 7c. Because 7c comes after 7b, those boosts are applied after Humility sets the baseline, so they do stack on top.

However, if another effect also sets P/T to a specific value in sublayer 7b (such as 'this creature's power and toughness are each equal to X'), the timestamp rule (CR 613.7) determines which setting wins: the more recent effect applies last and takes precedence within the same sublayer.

Concrete example: You control a 2/2 creature under Humility (making it 1/1). You cast Giant Growth targeting it (+3/+3, sublayer 7c). The final result is 4/4 — Humility sets it to 1/1 in 7b, then Giant Growth adds +3/+3 in 7c. Humility does NOT override the Giant Growth boost.

Relevant rules: CR 613.3 (layer 7 sublayers), CR 613.7 (timestamp rule for same-sublayer conflicts).