#siveure

[magicjudge]

Can I use alesha to return sylvan advocate with 6 lands in play? I'm not sure if the advocate's ability works in the graveyard.

Abilities of permanent cards only function while the card is on the battlefield unless an ability specifies moving itself from a non-battlefield zone or specifies that it works in a non-battlefield zone.

Sylvan Advocate is just a 2/3 in your graveyard and can be returned by Alesha.

[magicjudge]

How do X spells interact with abilities that check cmc on cast/ on the stack? I was told that eidolon of the great revel triggers on x spells even if x brings the cmc above 3, and this seems weird.

What you were told is incorrect.

Effects like Eidolon of the Great Revel or Void Winnower look at the total CMC including the value of X.