already in notes: Any creature with a positive attack value and is not in stasis, frozen or otherwise able to make an attempt to attack is added to the block value of the shield.
they key is "attempt to attack", not "successfully attack"
T1: 5 Giant Frogs attack (first turn, no damage reduction)
T2: 5 Giant Frogs attack (shield prevents up to 5 damage each, 0 frogs do damage)
T3: 5 Giant Frogs attack (shield prevents up to 5 damage each, 0 frogs do damage)
...
T1: 1 Golden Dragon and 5 Photons attack (first turn, no damage reduction)
T2: 1 Golden Dragon and 5 Photons attack (reduced by 6 damage, dragon does 4 damage)
T3: 1 Golden Dragon and 5 Photons attack (reduced by 6 damage, dragon does 4 damage)
T4: 1 Golden Dragon and 5 Photons attack (reduced by 6 damage, dragon does 4 damage)
but if say there is a voodoo doll or a creature with antimatter on the opponents side, they do not increase the block value of the shield. so if there were:
T1: 1 Golden Dragon and 1 Photon (first turn, no damage reduction)
T2: 1 Golden Dragon and 1 Photon attack (reduced by 2 damage, dragon does 8 damage)
T3: 1 Golden Dragon and 1 antimattered Photon attack (reduced by 2 damage, dragon does 8 damage)
T4: 1 Golden Dragon and 1 antimattered Photon attack (reduced by 1 damage, dragon does 9 damage)
...
so the shield adjusts if you either kill, antimatter freeze or otherwise reduce the number of creatures with positive attack value that will attempt to do damage the previous turn.
this shield is weakest against decks with a small number of powerful creatures, especially ones with grow. it is strong against decks which utilize swarms. in that way it is kind of the opposite of bonewall which is strong against a small number of strong attackers, but weak against swarms.