In all seriousness
Sandro - Left back is a weak position for us. We need the best solution money can buy. Sandro is a complete fullback.
Alderweireld - PL proven and world class. No brainer.
Mahrez - We're impotent on the right hand side. Valencia defends okay and runs with the ball but provides no real attacking threat. Mahrez can cut in, go wide, take players on, has proven it for a couple of seasons now. He'd also get rid of the predictability we suffer from.
World Class CM - This needs to be the signing we break the bank for. Get in someone that can link up play and support Matic, allowing us to give Pogba a more attacking role. I didn't want to put down Veratti or Kroos because i think they're both unatainable, but someone of that calibre is what we should be aiming at.
We could also do with a RB, but it's unlikely to happen this summer.
I am a big fan of getting young talent (Tierney or Sessengon), People have mentioned De ligt recently who is also a great prospect, but we don't have the wave of success required to take such risks. If you have a winning established side, you can bring in young players and groom them - right now i think the pressure is too high for us to do that.
I do think we need these type of players in our squad, but we need to have a clear out of our current squad players before talent like this can be bought in to fight for a first team spot. At Manchester United nobody should be guarunteed a first team spot, our "second string" should try and incorperate as many "first team alternatives" as possible. We have that in 3 positions, goalkeeper, striker and left wing, we should try for a few more.