It is rarely good to have an AD carry unless they are soloing top lane. The only one I would ever suggest would be Caitlyn as she can survive almost any gank by shooting her net through the wall. Vayne is sometimes viable if the other team is absurdly tanky.

How would you build Mundo in 3s?

I used to play Nocturne a lot in 3s, I would get boots of mobility and focus ms/as. It was very powerful as you could farm faster than pretty much anyone and gank anywhere at any time. This was mostly in Season 1. Not saying it's the most viable build, but I noticed you didn't mention him at all. Where do you think his viability lies in 3s ATM?

To clarify my build was typically rush lantern, boots of mobility(had ms quints and as/mres runes) and then depending on enemy I would build BC or PD then go from there. Like I said not really ideal but it would wreck people and get me farmed up quick

I don't think I'd ever build Boots of Mobility on TT, as you don't really need them. The map is so small that you'd be better off with Boots of Speed or Mercury Treads. Wriggle's Latern is a great item on 3v3 because you need map control and it is incredibly cheap. It pays for itself. Black Cleaver is decent and so is PD, I'd suggest BT as well though. He can jungle well in 3v3, and maybe top lane sometimes.

thoughts on ap/tank malph top lane and gp/panth bot? got me to silver rofl.

lmao XD peoples questions want answers!!! and seriously hes giving you guys tips on the map not the for each character you decide to use... im sure there is another post for that...

Gangplank and Pantheon are both very strong champions on the Twisted Treeline. Pantheon has great damage and a solid stun / jump, as well as good harass with his spear. Whereas gangplank has great survivability and mobility, while at the same time having great harass with his gun.

The combination of both their global ultimate makes for a great combo. It's a great combo to have pantheon start his ultimate, and before the other team sees the ring, have Malphite blow his ultimate, knocking the rest of their team up. As soon as they hit the ground have Gangplank use his ultimate so that they are slowed and it makes Pantheon being able to land on them absurdly easy.

Malphite is generally a very good counter to AD Bruisers. The problem is that he is far more of a tank and less of a magician to be able to have enough mix of magic damage and attack damage on your team. I can see this team composition as being a 'pub-stomp' type of team, but as you progress in rating into the 1500 and 1600s, I think you'll find that by mid game the other team will all have Warden's mail and you won't be able to scratch them.

Although it is a very cool team comp that I do think would be fun to play.

Suggestion: Try having Gangplank jungle, Pantheon solo bot, and Malphite solo top.
Or have Malphite jungle, Pantheon top, and Gangplank bot,

I don't know how to answer this / if it needs to be answered

What the teams should be doing before the minions spawn? What kind of strategy diversity there's to it?

I don't have a question yet, I just want to say I appreciate you taking the time to answer these questions to the community. It is nice to see someone giving freely because they want to help people.

If you have a jungler, you should be heading to your side's middle bush, in order for one of your teammates to leash the camp and the jungler to take them out. You all stay in that bush together in case the other team rushes you. If they rush you, then you will have the jump on them as they can't see you in the bush. It is very important when your bot lane (who is soloing) heads back to lane that he go backward and then down instead of to red buff and down to get to lane.