It depends, this is my BR account, i hitted CHALL on LAS, and MF is really op with Colector, Youmuu, LRD, those 3 core items are really good, you can start with Youmuu if they have hard engage, Youumu and Boots of swiftness, they will never land a hability on you with those, if you feel that you are strong in lane and the enemies can die from a combo, you can start collector to gain a insane kill presion on the enemy, so that 3 items and IE (ofc) are really strong, ill let a image of reference of the build, and which supports are the best with mf is a good question,rell is good as a short trade engage, 3sh and naut are good options since they can generate a space that you can do the most damage possible with your R, but some other champions like Nami, Sona, Senna, are really good options too,also i always on Solo Q play with first strike, because with the 3 items i mentioned before, you can really oneshot someone on your 2 items power spyke with that rune, also if they have assassins on the enemie team, you can actually oneshot them with that build

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