Rumble Club

Alright I'm going to describe a little about how you actually buy and use the cards, because I lost a whole bunch of brawler's gold buying cards and not getting in on the fights before I figured it out.

You do not queue with rumble cards the way you do with challenge cards. Buying a rumble card does NOT give you a dialog on the bouncer asking if you want to queue with your rumble card. Instead, when you buy a rumble card, everyone who is currently in the queue will get ported down to that rumble fight next. (You are cutting off the queue order entirely - the current fight will finish and then your rumble will be next.) Additionally, if you happen to buy a rumble card right when a fight is ending or in between fights, that rumble will then occur whether or not you yourself have hopped into the queue. So, make sure you hop into the queue BEFORE you purchase your rumble card! You will then be in the rumble, and you won't even lose your place in the queue after the rumble is over.

Another weird thing is that the card will NOT appear in your bags, unless there's another rumble queued up before you. Don't worry, lack of card in bags after purchase just means that your rumble is next. If a card does appear in your bags, another rumble is coming first.

Finally, if you have reached rank 8, you can no longer queue for fights without buying a challenge card. However, the rumble cards do NOT count as challenge cards. Just buy any old challenge card for 3 normal gold (I used Oso), queue up with it, and then follow the instructions as above.

Good luck!

Just completed this achievement, seems stranglethorn is the only difficult one but you can trivialise it with pet classes.

Mazhareen - tank and spank with enough players, otherwise I imagine its quite the dps check
Grief Warden - fixated player needs to kite while you kill it.
Battle of the Brew - you can just kill the 3 guys before they drag a cart to the middle and you win, otherwise drag a cart to the middle before they do.
Mindbreaker Gzzaj - Interrupt shadow bolt volley, I think there was a void zone ability, hes sort of like kozumoth.
Senya - need to kite while he has stacks, after each successive fixate channel he will drop a stack, after 5 stacks drop blow cds and kill him while he takes 200% inc damage.
Slippy Stampede - spawns a slippy(dippy's big brother) for each player in the rumble, he will occasionally get mad and dive at you and knock you in the air.
Stranglethorn Run - survive until the 2 minute enrage for a brawl comes and this one is over, you get stripped of all your gear and set to lvl 1 so you need to avoid all the mobs, they despawn eventually but you can stack pet classes and the pets can just one shot the mobs.

Hope this helps.

If you are having trouble with Stranglethorn Streak, use [item=104321] or [item=118936].