Replaying Yogg-Saron

Yogg-Saron reads:

Cast a random spell for each spell you've cast this game (targets chosen randomly).

My question is: Let's say I've cast 10 spells this game. I now play Yogg-Saron, and he will cast 10 spells for me. The last spell he casts is a Shadowstep/Vanish (something that returns him to my hand).

If I play him next turn, how many spells will he cast for me? Still 10 (because I as a player did not cast any more), or 20 (because Yogg reads 'cast')?

Solution 1:

Yogg-Saron counts only the spells cast by the player for its battlecry. Spells played by a previous activation of Yogg-Saron are considered cast by Yogg itself, so they don't add to the total (as you can read in this official tweet).

So, in your example, the second Yogg will cast only 10 spells.