Alchemist/Hellcat is core. That loop is insanely powerful - get one charged and you can charge the other and Gard and likely have one of them ready when you finally cast Gard, so you can keep going after.
I’ve tried Mercy and Loyalty - Loyalty seems easier to keep it to two hits with Gard due to the increased armor gain, but Mercy is likely faster if you get a good starting board. One could also just go through some extra loops first to make up for Loyalty’s armor. Having a blue troop isn’t critical since you have two transformers already. (Mercy also nabs a +2 armor gain for having two Whitehelm troops, if that matters…)
I actually prefer Brown/Yellow banner for this team over Dragons’. Charge Alchemist in two matches of either Red or Brown if one is a surge, three otherwise. All Dragons’ banner gets is two guaranteed if they’re both Red, but can’t charge in one match which would be cool. Also means its easier to get shut out if the board is devoid of Reds.