Since Doom is a type of "war horse" and the best one suited for PvE & PvP, those elements should be enhanced.

1)

Change flames from red to BLUE (to indicate a hotter flame)

2)

Give Doom an addition +8AP (with room to grow up to +30AP, since you are setting high bars of 290AP and 340AP for players!)

3)

Reduce fall damage by 20-30% (so we can jump off of small mountains and high hills with less risk of dying)

4)

Panic mobs for 1 second when stomping at them to spew fire on the ground (since most living creatures litearlly panic when set on fire)

5)

Make it look more menacing and fearless, taking clues from Sleipnir (Odin's horse, which is perhaps the greatest WAR HORSE in mythology)