I was playing Druid vs. a Warrior. He does this play -> Korkron Elite -> Inner Fire -> Bloodsworn Mercenary -> attacks for 12 to put my health at 11 then plays -> Teron Gorefield to set up lethal then passes the turn to me. I have 9 cards in hand with 2 Zephyrs The Great in hand and I have 10 mana! I want to set up for the 0 cost priest silence to counter the lethal setup. First I play -> Khartut Defender for 6 then -> Zepher’s the great for 2 leaving me with 2 mana, these are my options; holy light for 2, Tirion for 8, and healing touch for 3. I should of had a silence but got screwed, so I play the 2nd Zephrys for 2 putting my mana to 0 which should guarantee me the 0 cost silence! I get screwed AGAIN!!! He offers me the same exact 3 choices. Luckily for me my opponent conceded during my choice selection thinking that I had it when I clearly didn’t. I have screen shots of the encounter if you would like further review. Please help.
Zephrys does not know about special text on cards in play (with one or two exceptions, I can think of Doomsayer). All it sees is a well-stated 3 mana 3/4 with deathrattle. It probably does not assume it to be a threat (at 5 mana 2/3 with deathrattle might be different, it might realize the deathrattle will have a big impact). See this for more insight into how Zephrys valued Deathrattle at the time of that post 4 months ago:
https://www.reddit.com/r/hearthstone/comments/egijk0/i_found_out_why_zephyrs_doesnt_like_silence/fc7vnmc/?context=3
That being said, you did the right thing setting it up so you can play Zephrys with 0 mana left. It is quite possible that Zephrys offerings can be improved, especially when dealing with Deathrattles. But remember, some Deathrattles give negative effects to the card’s owner, so in those cases silence would be counter-productive, so it is a delicate situation.