As of time of writing(12/31/2020) there's not a lot of information on Rubicks interactions with chard abilities.
After some checking, some odd behavior was found:
- If Rubick steals dragon knights elder dragon form while Rubick has a shard, Rubick will gain fireball alongside dragon form. If Rubick does not have a shard, he will not steal fireball. However, if rubick casts spell steal on dragon knight after dragon knight casts fireball, Rubick will steal nothing and will lose all stolen spells. This seems like a bug.
- It appears that some abilities, like earthshakers fissure, will benefit from Rubick having the shard(cooldown will be reduced) but the effect is lost once a different ability is stolen, even if the effect(in this case the fissure on the ground) still remains. Unclear if this is a bug or working as intended, but it's certainly confusing.
- Stealing abilities that have a shard upgrade, such as Enchantress' Nature's attendants or Pheonix's fire spirits ability will give you the upgraded part of the ability, if the ability has it, as long as you have the shard. This works even if the enemy hero does not have a shard.
- Passive abilities that gain an active component, such as Nightstalkers hunter in the night, cannot be stolen, and instead the previous spell used before using hunter in the night will be stolen.
- Simple new abilities like Pangoliers roll up and Alchemists shard ability can be stolen even if Rubick does not have a shard.
- Abilities that interact with other abilities, such as Slardars Slithereen Crush, will also apply the secondary ability(corrosive haze) if Rubick has a shard.