Love the idea, been wanting to jam new Sarkhan into a superfriends deck! Some thoughts:
1)
Magmaquake is a bit of a nonbo with all the planeswalkers you're trying to run. I would suggest
Earthquake instead.
2) 21 lands is not enough to reliably hit land drops up to turn 5, let alone 6 or 7. Would suggest a minimum of 24 lands, probably 25 considering the number of 4 mana spells.
3) As has already been suggested, Snow-Covered lands are advisable if you want to use
Extraplanar Lens as it denies your opponents double red mana.
4) I would consider cutting some utility cards for better card selection/ draw. Just 3 or 4 cards like
Faithless Looting,
Tormenting Voice etc. can go a long way towards making sure you hit land drops and don't have dead cards in your hand.