Not enough draw for a ramp deck that also uses mandrake, also i personally don’t like mandrake in that type of list. Also not enough 2 drops, i like having 9 despite having flash, Gro is kinda meh because magmar relies on their 4 drops a lot. Prolly add Silithar and shroud, get rid of mandrakes, an earth sphere, gro. Get rid of the 2 Chrysalis for one taygete and one Lkian. Basically Gro can be decent and Mandrake is really good, but not if you are aiming for the late game which you are with the earth spheres, the plasma storms and the elders. Gro is nice in Floodlists where you don’t need to accelerate into 4 that much and Mandrake is ridicolous at 7-9 Mana, great in midrange and aggro.
Also Slow Magmar isn’t the best way to go really. Aggro and midrange are better.