This jungler and mid duo have a ton of burst damage and can chain their CC for powerful combos; let’s break their synergy down.
Vi is a very well-rounded Jungler. She can clear the jungle pretty quickly with the AoE damage from her E and the mobility of her Q, and gank effectively by using her Q to engage enemies. If you need extra range to land the Q or want to catch enemies off guard, Q+Flash can be used to extend the range of the Q. Once Vi reaches level 6, her point-and-click ultimate is an easy and powerful ganking tool and can completely lock up an enemy. Her Q can then be used to get in range of enemies to follow up with an ultimate.
Annie is a relatively simple mid-laner but has strong damage and multiple CC options. Farming with Annie is quite easy, as killing a minion with her Q refunds its mana cost and half its cooldown. Her W can be used to push out waves, while her E can help you escape a gank or catch up to a fleeing enemy. It’s very important to track her passive stun -- which can be done using the 4 bars underneath her mana bar -- as you should save your spells for enemy champions when your passive is available for a free trade. Upon reaching level 6, Tibbers deals a lot of AoE burst damage or can be used in combination with Annie’s passive for an AoE stun.
Thanks to how consistently Annie can stun a target, this can be used to set up Vi for ganks. By stunning a target with your Q/W while your passive is up, Vi can easily follow up with her Q for a ton of damage and an extended CC chain. If the enemy manages to escape, Annie can use her E on Vi to help her get in range to land more basic attacks and E’s.
Once you’ve unlocked your ultimates, they can be chained for another potent CC chain: Annie can Flash/Tibbers when her passive is up to stun multiple enemies, and Vi can use her ultimate to lockdown another target and displace the rest of the team she travels through.
Runes and Items
Taking Hail of Blades as Vi's keystone increases her burst damage and makes it easier to proc her W, while Sudden Impact can be procced every time Vi uses her Q to enhance her skirmishing power. Vi can build a plethora of items depending on the state of the game. If she's ahead, she can focus on damage with items like Divine Sunderer, Eclipse or Death Dance, and if she's behind or is the only front line on a team, can build Thornmail or Guardian Angel to become a tank.
Annie's keystone choice is pretty flexible, and can take Arcane Comet to increase her poke damage, Eletrocute to make her burst damage even stronger, or Predator to become a mobile ganking threat. As for her items, she builds standard AP mage items like Luden's Tempest, Rabadon's Deathcap, Shadowflame and Zhonya's Hourglass.
Vi and Annie synergise together due to their incredible burst damage and ability to lockdown targets with multiple forms of CC. Ganking's Annie's lane as Vi is pretty simple if Annie can stun the target before Vi ganks, and the combination of their ultimates can single-handedly win a team fight.