I think as a standalone card, this is underwhelming and would not see any play
The Haunt of Hightower grows every time a card hits an opponents graveyard, while Quest for the Nihil Stone builds up to deal repeated damage once your opponent is out of cards
In most cases (see below), if you wait until the combat damage step or end of combat step, it will be after combat damage has been dealt, so the Ninja won't deal combat damage
Imagine giving your Sol Ring cascade with TARDIS and not having a nonland permanent for zero mana in your deck
Magic: The Gathering Assassin's Creed Preview Events Debut and Previews Begin on WeeklyMTG : June 18 Card Image Gallery and Previews Complete : June 21 Global Tabletop Launch : July 5
Hellspur Brute Nothing too exciting here, but we probably shouldn't ignore a potential 5/4 trampler for 1 mana