Ragnaros is the third legendary card, and first old legendary, to get the Diamond treatment!

When Patch 20.2 drops, anyone who has collected the full set of Classic legendary minions will be able to unlock the Diamond Ragnaros card. No animation preview is available right now, but we're confident that post is going to strike us with some amazing visuals.

Hearthstone Patch 20.2 drops next week and contains large updates to Battlegrounds with the introduction of the Quilboar tribe.

Quote From Blizzard

Diamond Ragnaros has been added to the Tavern! Diamond Ragnaros can be acquired by completing the Classic Legendary Collector 5/5 achievement (Collect all 36 Classic Legendary cards). Please note that players who have already completed and claimed this achievement must reclaim the achievement to obtain Diamond Ragnaros.

We’ve also added a new progression achievement, Tavern Regular, which tracks total reward track levels earned on your account across all reward tracks from each expansion. Completing each tier of this achievement will reward a choice from 1 of 10 new Hero skins, featuring upgraded armor!