Three to One
The two techniques Ryu had found were [Grave Digger] and [Death Swap].
[Grave Digger] was quite an interesting technique, especially when used either cleverly, covertly, or on a chaotic battlefield. It gave a corpse puppet the ability to dig and move through the ground quickly, almost like an escape technique. But, this was instead used to place a corpse puppet in position to attack.
Images of skeleton hands piercing up from the ground was definitely one that was synonymous with this technique and the possible combination uses of it didn't need to be explored. It was definitely quite the technique if paired with the others Ryu had taken.
[Death Swap] was likely the most complex technique Ryu had found to this point. [Reanimation] wasn't very difficult to use, or else it wouldn't be known as the Origin technique of Necromancers. [Death Swap] definitely left it far behind in terms of complexity.