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Im sure most of the people have their own propositions in mind, but those in the first post are universal restrictions and we should keep the discussion in that way.
Also, let's forget Pokemon and OU metagame is not only played in showdown but in live tournaments with Nintendo Switch and...
Before an outright ban, I would prefer to give it a restricted chance by:
Limiting the amount of Pokemon on any given team that have access to possibly Terastallize during a battle
Only 1 can be terastalized. In Teambuilder, this should be easy to code with a simple checkbox
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