Not discussing viability per se, but kind of.
The most recent iteration of Dragon combo uses Tasigur plus Collective Brutality. To actually execute, you do need a lot of mana. This is currently not really possible online with out timing out.
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Is there a build of Dragon that is playable online?
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What other decks suffer from this same phenomenon (playable in paper due to short cutting a loop or similar short cut, but not online)?