There's a whole post about this: https://community.gemsofwar.com/t/gold-farming-in-explore/65463
City of Thieves delving is A Thing, and also delves in particular have a buff mechanic we've been utterly ignoring. To wit: Delve Questions (on Reddit)
In The Deep Hive, we want to burn Portals to get Queen Beetrix because she's effing broken. Having faced her in PVP now, yikes. Alternately, in Amanithrax there's King Gobtruffle, who has the whole "I'm a gobbo" thing of guaranteeing an extra turn. We actually have a gobbo teams, so.