@Grabby the Squid, especially at two star, is incredibly valuable. As for the second relic, go nuts, I think @Ardent Songbow also at two star is also incredibly valuable since Felix loves to use his cooldowns as much as possible during a fight.

One of Felix's larger problems is engaging and then getting juked out by the opponent. More often than not you need to dedicate a movement ability to get up close to whoever you are wanting to fight, which they will usually try to disengage by using their own movement ability or self peel ability. @Grabby the Squid is incredibly powerful as that first movement ability to engage or just to follow up their movement ability. We're basically added 1 or 2 dashes depending on what star your @Grabby the Squid is to a hunter that desperately needs as many tools as possible to stick on the enemy. It is also very worth noting that @Grabby the Squid roots the target while you are traveling to them, so if you land a grapple on them, it is very easy for your teammates to follow up since you have shortly locked down the movement of the enemy player.

And now, the antiheal problem. A fair share of the characters that are currently meta in Supervive apply antiheal as part of their kit (Brall, Shiv, Kingpin as examples of strong characters that apply antiheal while fighting them). Because of this, vamp based Felix builds are not particularly strong in my opinion. The concept is there, but fighting most meta hunters completely shuts down the build. CDR based Felix builds are significantly stronger- rather than relying on omnivamp to keep yourself alive and health, you are using your CDs (specifically your Q) to generate shields. The goal is to spam Q as much as possible, which @Ardent Songbow and more CDR focused builds can help provide. It also very important to mention that Felix knocking an enemy full refunds the CD of Q! Felix is highly incentivized to run around and knock as many of the enemies as possible in a fight to easily chain into the next person. That being said, I still include @Gorger Talons to this build because if combo'd with your Q at max hp, you get an absolutely fat overshield. You could play @Burning Palm or honestly follow your heart if you don't care for @Gorger Talons. It is the only vamp we really bring into the build, and it by itself is quite valuable. @Chrono Gauge is used for more CDR. @Rocket High-Tops are effectively the best boots that you can get on any champion, we all love our movement abilities being just that much more effective. If you find some @Mecha Boosters then I would definitely swap out the @Rocket High-Tops for @Mecha Boosters.

As for the perks: Honestly, run what you want. I included some decent suggestions. I always bring @Thermal Suit in endgames that are going to include lava specifically, as tapping lava hinders Felix pretty significantly by immediately applying antiheal. It grants you movement and freedom to walk around and not be as restricted as other players might be, and we want as much freedom of movement over our opponents as possible. You just run whatever you think is interesting or want to try out. I would recommend @Glider Coolant as it improves your ability to abyss fight on this character, which is already pretty poor. It also allows you to use your dash + glide at opponents more aggressively without fear of being punish spiked.

Armory

Hyperhaste

Armory

Hyperhaste

Builds Using Hyperhaste

Builds Using Hyperhaste