10 Nov 2020
You can't pay {3} more than once to put more than one +1/+1 counter on the attacking creature.
10 Nov 2020
If you choose to pay {3}, a second triggered ability triggers. Players may respond to that reflexive triggered ability before the +1/+1 counter is put on the creature.
10 Nov 2020
Anointer of Valor's triggered ability triggers when any creature attacks any player or planeswalker.