Thank you for your comment! So about Malzahar vs Senna in Mid lane? I honestly never faced her in Mid lane including other mages as well like Viktor since I main him. I don't think anyone plays her in Mid lane since she is mostly played as a Support or even as ADC. If you do however face her as Malzahar in Mid lane, then I suggest not to poking her early before you get some items. If you try to trade her, she will outrade you back with auto attacks. Avoid her Piercing Darkness and Last Embrace. Just focus on farming, Malzahar is weak early game and has mana problems early if you spam a lot. After you have Lost Chapter and you didn't die to her and her ganks, then you can begin to poke her. Save your Nether Grasp when your jungler is arriving and you will defenitely get a kill since she is very squishy champion. You should also buy early Seeker's Armguard especially if their enemy team is full of AD. Once again, don't trade her early, farm for late game, poke her after firs back, avoid her abilities, don't trade her with autoa attacks, win. That is all I can give tips against her.

If you got any other questions, feel free to ask me! :)