Lethal requirement to get summons is a mechanic that is generally too narrow to be a viable part of any strategy. Also, since his boost ratio is based on static elements, hitting that lethal damage mark will get harder and harder. Hes another mythic that will always drop the turn and the traits nonsensically conflict with each other.
One good point about him is he has completely zero conflict with both the thing he summons and the legendary that boosts him to 50% start and is fed by one of the colors he creates. But the synergy ends there because Gar’Nok puts the board in a state that severely weakens the shade, and taking chip damage from Gar’Nok is a pretty poor way to fuel the Shade’s mana trait otherwise. Burning should activate it, like other Orc traits, but unfortunately, its more common to be stunned nowadays than burned. On the one hand, he’s another stealthy (technically) summoner, but requiring his spell to deal lethal damage to do so (and drop the turn) generally limits the summons to usage as “meat shields” to stall for his particularly unimpressive damage (think Euryali, who actually has decent damage and stalling like this can occasionally net a win versus teams that don’t chain well or that you have already broken their synergy) rather than putting you firmly back in the fight (like Arachnean Weaver, who can turn a single well-timed kill under the right conditions into a win).
This troops design seems to be meant to have a “comeback factor”, but he’s missing the main tools that make that kind of thing possible - namely, a way to chain spells, sustain itself in disadvantage state, or turn a single opening while in disadvantage into something that can lead to a victory. I think in order for him to even function like this, he would have to bring his summons in empowered. This would allow him some level of board mod by proxy that synergies back with his boost ratio. Alternatively, he could grant a fixed amount of mana to every Fist of Zorn on your team after his spell is cast (including freshly summoned ones). A better trait for him under this set of cirumstances would be to gain mana when skulls are matched (by any ally). I think that would fill out his kit. Even that would make him an extremely niche setup (since you need allies to dive headfirst with skulls to set it up, or have ally deaths) unless whatever the (eventual, not even planned in spoiler data for the next 6 classes) Orc hero class gets somehow supercharges them to unbelievable levels.