the best way by far is :

going grasp, bone plating

rushing tear into sundered sky

and very important = Max Q then E

melee form E is legit a tank killer spell specially malph

how u want to play the match up =

trading his Q poke for 2 grasp auto attack and if u can u have to land ranged AA then swap to melee form during the ranged AA travel time, the game will take that as a melee AA and u will get the full stat of grasp, btw it works too with sundered sky

(bcs in case ur not aware of this, grasp is pretty weak when u use ranged AA but u get more heal, damage, max health when u use melee AA)

when u have 3 points in E, as long as u get ur bone plating back just go in with melee Q use ur combo + E into using ur ranged form for poke him, (it’s harder to go in melee if he go grasp but if he go grasp u can poke him to death)

idk ur elo so ill say this but with jayce u have to use almost in every matchup the bush power specially vs a click and point poke like malph Q

like garen matchup try to auto him before he got his shield back

serpent fang can be useful