This is a guide to a really good, trapping team the idea is that Blitzcrank and Veigar lane together and Jarvan and Kog,maw lane together and the mid should either be oraka (for her round the map heal), Ashe (for her unlimited range arrow) or Karthus (For his hit everyone on map ulti) if karthus or Ashe then the idea is to be cautious, farm minions kills in mid and when get ulti keep an eye on team mates and if someone manages to escape your team with very low health use your ulti, same for soraka except use ulti when team is in trouble, anyway, blitzcrank and veigars tatic is for blitzcrank to use Rocketgrab to pull people towards the turret then for veigar to use event horizen in order to trap or slow them, if the turret doesnt look like its going to kill them viegar uses his ulti if hes got it and can immediatly after event horizen to cause as much damges as possable then let the turret finish them off.
The idea of the team of Kog'maw and jarvan is for Kog'Maw to use void ooze in order for jarvan to be able to use his ultimate better then when oppenent is still stuck inside jarvans ultimate wiuth jarvan attacking them kog'maw can use living artillary in order the finish them off quicklt

it doesnt really matter as long as you follow a build for one opf the characters you are playing and get a few slowing items

When in team fights Blitzcrank should try to pull one away from the crowd and towards the turret and the team should kill him there uusing blitzcrank and veigar to stop him escaping (Blitzcrank can use power fist to give the turret approx 2 more shots), when it is 5 vs 5 and there is no way out of the situation continously slowly retreat while staying in xp range and doing as much damage as possable then when possable have jarvan jump on one with his ulti, his team should try to help and Kog'maw should use void ooze to set them up so veigar can gt them all in event horizen and then use his ulti to do as much damage as possable (if jarvan cant handle person he has trapped in ulti byself have whoever is mid help him) and then have blitzcrank get into the middle of them all as fast as he can and use his ultimate ahnd this should hopefully kill them or make them on such low health that you can either chase them down and kill a few or have karthus if on your team use his ulti to finish them off.