The power of the other creature is checked only when it blocks or becomes blocked by Arrogant Bloodlord. Once the Bloodlord’s ability triggers, it will be destroyed at end of combat (after combat damage has been dealt) even if the other creature’s power changes before then.

If Arrogant Bloodlord blocks or becomes blocked by a creature whose power is 2 or greater, Arrogant Bloodlord’s ability won’t trigger. It still won’t trigger if the other creature’s power changes to 1 or less later in combat.

If Arrogant Bloodlord becomes blocked by multiple creatures with power 1 or less, its ability triggers that many times. Each of those abilities will cause it to be destroyed separately (in case Arrogant Bloodlord isn’t destroyed the first time due to an Aura with totem armor, for example). The same is true if it somehow blocks multiple creatures with power 1 or less.