Well, the show was elusive on Kelly's birth and what that means as they were already focusing on Diana.

I always imagined Kelly as a supercharged hybrid with an amped up Grimm stare and crazy Woge.

Likely.

I think that he'd still have the weird eye thing that all grimms have on top of him being a wesen

I think he would be similar to Diana. Like he’ll have a glowing eyes. But also he will be a full Grimm. I think his Zauberbiest side will be similar to Captain Renards but without woge. He’ll have super strength and glowing eyes.

I’d like to think that Grimms are different than normal humans. In the series, being a Grimm is a 50/50 kinda of thing. Some of the family become Grimms and some don’t, like the case with Josh Porter who didn’t become a Grimm even though his father was.

Another way of looking at it is when a Wesen marries a human, their children have a 50/50 chance of being Wesen. Applying that logic and the genetics that are involved in Wesen mixed marriages where the prevalent Wesen species is what the child becomes, I think that there is a chance that Kelly is a Grimm and only a Grimm, not a half Zauberbiest.

Don't forget Nick got his Grlmm powers upgraded, ever since he was a Zombie Grimm.

Maybe, Kelly got that, like how Diana's Hexenbiest powers upgraded when Adalind was her powers back while, pregnant with Diana.

I personally think the Grimm DNA would cancel out the Wesen DNA, so I don't think Kelly would have any additional abilities but given he's hunting Wesen in 20 years I'd assume he's full Grimm. Maybe he's enhanced like Nick after he exposed to the Barons Zombie Toxin, that'd be cool. I mean the coolest option is for him to be a Zauber-Grimm with Grimm abilities and Zauberbiest telekinesis or something. I saw someone say Grimms only have the ability to see Wesen and that's not strictly true, Nick seems to possess some kind of peak human/enhanced physical abilities given how he takes down physically superhuman Wesen and keeps pace with them. It's implied on the wiki that Grimms have natural artistic and combat-related ability, and post-exposure to the black fly wesen and the Barons toxin Nick seems to gain further enhanced hearing, stamina and a kind of woge, which was cool. Anyways while the Zauber-Grimm possibility is cooler, I'd say Kellys just a Grimm. However he seems to prefer using Zerstorers staff, which has a lot of abilities that maybe he can access thanks to his heritage.

Stephynee.c he's not only Grimm ! Did none of yall pay attention!? His mom is a hexinbeast! So he is mixed with that and a grimm!