League of Legends (LoL) Question: Team Fights

When playing Teemo you are usually better off split-pushing. However, Teemo can have a stronger impact on team fights that involve defending an objective like baron nashor with proper Noxious Trap placement. Personally, I would stick to split-pushing most of the time and try to be as annoying as possible.

I don't exactly know if you're playing assassin Rengar or tank Rengar, so I will explain both. For assassin Rengar you should wait for most of the hard crowd control on the enemy team to be burned and then burst down one of the enemy team's primary sources of damage. It is very important to properly time when you dive on top of a damage dealer.

Tank Rengar has been growing in popularity recently, and he serves a similar role. Your objective is still to jump on to a major damage dealer; however, if you're tanky enough you can initiate fights. Initiating with Rengar can just be using an Empowered Bola Strike on a primary damage dealer that is a bit too far forawrd. However, initiation with Rengar is not very ideal unless your team has decent follow up crowd control such as a Command: Shockwave. As tank Rengar you do not have to be as patient about diving onto an enemy damage dealer because your objective is to switch the focus of the teamfight onto you. Tank rengar can be deceptively tanky with Battle Roar and Empowered Battle Roar allowing him to stay alive for quite a while.

In terms of team fighting items for Rengar, Guardian Angel allows Rengar to dive into a team fight burn his cooldowns, die, and once revived can use his abilities once again. Banshee's Veil is a great item for assassin Rengar against a lot of crowd control in order to prevent yourself from being immediately crowd control locked. Randuin's Omen allows you to stick to targets, and makes you a tanky cat. Black Cleaver is a decent item with a partner physical damage assassin.

Yeah teamfight tactic for Assasin Rengar is kinda easy just R click on adc Q empowered Q w e but he shloud be dead after second Q rengar has crazy dmg with BT Black cleaver

Teemo isn't really a good teamfighter. He is better off splitpushing enemy's turret while your team draws their attention.

For Rengar you should get items like Last Whisper and Bloodthirster, use On The Hunt jumo on enemy's ADC and burst him/her down. Then you can either start fighting with the rest of their team or run away and look for another person to burst down.

Guardian Angel, Randuin's Omen, Sunfire Aegis are good items for teamfights. Guardian Angel gives you some additional health (not full hp, just sliver of it), Randuin's Omen gives enemy debuff and Sunfire Aegis deals damage (noticeable only in the early game though.)