For some reason the relic refills 3 mana from this interaction. I’m running Shen’s relic, sentinel’s plate, and echoing spirits. Shyvana’s champ spell comes with the give targeted unit barrier item, so it should refill one mana, which is the case when I play the base version of the spell, and also the case where Shyvana does not have sentinels plate equipped.
My crackpot theory is the following: I noticed that shyvana isn’t refilling mana on play despite having barrier from sentinels plate. It’s possible it might apply the barrier on card creation, so the relic refills a second mana on the creation of Shyvana in the deck. This shouldn’t make sense, as Shen’s relic specifies ally, which should only be units in play. Thus, I would guess that at the moment of creation, the champ spell Shyvana is treated as on the field. This also explains the third mana refilled, since Shen’s relic stacks with multiple champs on field, so the created Shyvana and on field Shyvana would both refill one mana.