The stats are way too good on this minion. 5/3 for 4 is just 1/1 below hailstone golem in stats, but you’re playing this mainly for the dying wish effect, which is summoning a 0/10 with provoke that locks you in place until you can get rid of it. So if you count up the total stats then it becomes 5/13 for 4 which is disgustingly good. Compare this to Reaper of the Nine Moon - it costs 1 less mana in exchange for not having flying, but the dying wish effect is significantly better, because more often than not you’d rather want the 0/10 provoke than any random minion from your opponent’s deck.
In Lyonar it’s a staple, sure, but the problem is it seems to be a staple in every single control deck out there. No other dying wish minion requires a dispel or transform effect as much as this one. A 5/3 for 4 is very solid in stats (10 damage to your general), but it’s the 0/10 with provoke that is the key here that is a lot stronger than it looks. If it is left alone, it itself is a minion with 10 health and provoke, so if your opponent cannot remove it, then it locks them in place for 5 turns. If you are Argeon you can use your general power on it. If you are Vanar you can use mark of solitude on it, or razorback it for some extra damage. If you are Abyssian you can use deathfire crescendo on it, or shadow reflection. Any deck that has buffs will value Dioltas, because a 10 health minion that locks the opponent in place is very difficult to remove. The value that this minion brings is way too good for 4 mana, and if your opponent do silence or transform it, then that means they have less silence/transform for your other late game threats.
I think this card needs a nerf personally. I say make it so the tombstone no longer has provoke. Having provoke on a 0/10 minion that comes out of a well-stated 5/3 for 4 mana is way too much.