Hey Skeri! sweet Gitrog Tempo deck you got here
When looking through, the one card that came to mind was
Tireless Tracker. He seems like he'd be really good with all the extra land-drops off Gitrog. Lets you stack up a bunch of clues for when you have extra mana, and sacrificing those clues only makes
Bloodbriar bigger. Plus the deck seems low on 3 drops (though I guess with ramp that isn't a bad thing), so
Tireless Tracker could fit nicely there.
In terms of what to replace, the only guy that jumps out at me is
Permeating Mass. When your strategy relies on being able to get through with these giant creatures, giving your opponent the possibility to freely transform your win-cons into 1/3 masses seems risky. They may be good in the sideboard to bring in against Ulamog or something, but against tokens or CoCo,
Permeating Mass just seems like a bigger risk than benefit.
If you wanted to keep up the 1 drop count, maybe look into
Kessig Prowler. 1 for a 2/1 is already good for tempo, and being able to dump mana into him late game to make a 4/4 who can't be gang blocked seems like a nice alternative. Just something to think about.
I'm glad to hear
Bloodbriar has found a home in your deck! I hope it works well for you at FNM this week