PSA: Junglers, Dragon can no longer be ignored.
The damn thing gives an immediate, noticeable, power-spike. You don't even need to stack all the same kind, any dragon is a good dragon. And if you think "oh I can just let the other team have one or two". Yeah, keep telling your self that when they get an elder. All the sudden that one or two really really hurts. So please, be mindful of it, try to keep crab control, and don't just keep farming when it comes up. Give it a thought, maybe gank bot really quick to see if you can get map-control on it.
Same for Rift Herald.