Further brainstorming have led me to the conclusion that the Air Monolith's ability should cost 1
, because it is a reusuable ability and it's actually really strong when used in conjunction with Sky Blitz and can help creatures from other elements bypass Wings.
The Gravity Monolith's ability is just to punish Air Monolith's ability to give Airborne.
I felt that just making the creature lose airborne is UP, so a Gravity Pull effect is added. It's actually quite versatile; you can use it on your own creatures to defend you from damage or kill an opponent's creature.
Light Monolith does seem a bit UP, how about: "When Light Monolith comes into play, target creature gains +1 l +1 and its ability is changed to Light." < A lobo with a small buff. No more free buff to Dune Scorps and Deathstalkers. XD But then if this is done, Aether Pendulum might need a different ability because this is overshadowing Aether.
Fire Monolith should be a mini Rage Elixir: "When Fire Monolith comes into play, target creature agains +3 l -1."
Water Monolith: "When Water Monolith comes into play, removes 3 Poison counters from the target player. Gain 1 Purify counter if not poisoned."