In case this helps here's a list of ways to (realistically) get past this shield:
Creatures that could be realistically buffed into the range where they can hurt you:
Pegasus (with 2 or more blessings)
Wyvern (as Pegasus)
Light Dragon (with blessings and/or rage potion)
Ruby dragon (with blessing or chaos power, rage potion would kill it)
Anything (with momentum)
Growth creatures:
Forest spirit (would take 7 turns to grow large enough)
Fire spirit (would take 8 turns to grow large enough)
Oty (must eat 16 creatures -> would never happen)
Vulture (15 or 16 creatures must die, very rare to see one this big)
Lava Golem (probably the most credible threat of the growth creatures, but it would still be several turns before it became a threat)
Creatures that could hurt you unbuffed:
Sapphire Charger
A few mutants
Flying Titan
Crysodora
Weapons or spells could hurt you, but if there's any healing involved only
and
could have a reasonable shot with these.
could have a shot with momentum.
might be feasible with arsenic, but not likely.
That may look like a lot, but most of the buff-able creatures require 3 or more cards in 2 different elements, and almost all of the growth creatures would most likely take 7 or more turns to get big enough. A fallen elf could take care of almost any creature that could get through the shield if it wasn't quinted or have momentum.
I didn't bother listing things like photon + 5 blessings, since these are not realistically feasible.
Let me know if I missed anything.