The front side of Valentin, Dean of the Vein is certainly a solid play in the first turn or two, but its the back side of the card, Lisette, Dean of the Root, thatll do a bunch of work for your deck, boosting all your creatures whenever you gain life, assuming you have the mana available
Most of the value here comes from the activated ability, which is a good way to get value in the late game since you can get 4 counters at a time
Either your opponents get dead quicker, or youre going to be targeted out
* Return two target creatures that share a creature type from your graveyard to your hand
Of course, Davros is good friends with Ob Nixilis, the Fallen, Shrieking Affliction, and Tempting Witch