This is the Spikeridged Steed HS Paladin Card from the Journey to Un’Goro expansion due for release in April.
It’s a Paladin class spell and the card reads: Give a minion +2/+6 and Taunt. When it dies, summon a Stegodon.
You can get Spikeridged Steed by opening packs from the Journey to Un’Goro set.
*Another card with some Paladin quest synergy.
Here is the Stegodon token summoned by the Spikeridged Steed target dying.