Vandal Savage is a very powerful foe and it will take two nights and a group of superheroes to take him down. In "Arrow" season 4 episode 8 titled "Legends of Yesterday," Oliver and Barry attempt to find a way to beat the dangerous immortal.

The installment serves as the second part of the "Flash/Arrow" crossover event. Here, Barry seeks the help of Oliver to keep Kendra Saunders aka the future Hawkgirl away from the clutches of the new deadly foe. The Arrow, always ready to help, had Vandal's target stay in a secret location.

As they buy time before Vandal gets to Cisco's lady love, the entire Team Arrow and The Flash put their heads together to devise a powerful weapon that will ultimately destroy the big bad once and for all. However, with a foe that just won't die, victory may not be on the side of the heroes this time.

Notably, Vandal Savage will be the baddie in the "Arrow" and "The Flash" spinoff "Legends of Tomorrow" premiering January. This means that the immortal villain will be the problem of the motley crew of good and bad when the new series starts.

But that doesn't mean Barry won't have fun fighting Vandal. In a promo picked up by Screen Rant, the scarlet speedster delivers a lot of banter as he and Oliver take on the enemy.

Meanwhile, Oliver will have more than just an undying bad guy wreaking havoc and messing up time and space as a problem in the upcoming "Arrow" season 4 episode. Executive producer Greg Berlanti told TV Line that Oliver's son will come into play to complicate things.

In the flashbacks, it was revealed that reckless and playboy Oliver has a child with a former girlfriend. However, Moira bribed her in exchange for leaving Oliver alone. This issue will re-emerge in this week's "Arrow" season 4 installment and Felicity would not like it in the least bit.

"Arrow" season 4 episode 8 "Legends of Yesterday" airs Dec. 2 at 8 p.m. ET on CW. It is preceded by "The Flash" season 2 episode 8 "Legends of Today," which airs Dec. 1 in the same time slot.