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.
Is there a build of Dragon that is playable online?
What other decks suffer from this same phenomenon (playable in paper due to short cutting a loop or similar short cut, but not online)?