I've said it before and I'll say it again: shield counters are bad and encourage toxic behaviour. I just faced a deck that all they did was use spells that turn lands into x/x creatures and then enchant that with shield counters. They create a 10/10 creature and put shield counters on it, you kill the creature and they put a shield counter back on it again before it actually dies then even if you're able to kill it again before next turn they put another shield counter on it so it doesn't actually die and if you somehow manage to survive that attack and are lucky enough to have something to kill it it doesn't matter because you didn't actually kill it you just killed the counter and they put another one back on straight away.

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This is a problem for gameplay balance, no? To have literally unkillable creatures? It sure as shit feels pretty unbalanced.