For zaerog farming.. goemon teams can work really well, especially because you can be very precise about HP and damage you take turn by turn allowing you to setup your gems pretty effectively...
3 High Gems to start... either at 2 or 1 delay. Dealing 6990 dmg per attack.
Possible turn 1 delays: 2 2 2, 2 2 1, 2 1 1, 1 1 1
Damage taken on turn one(percent chance to occur): 0 (12.5%), 6990(37.5%), 13980(37.5%), 20970(12.5%)
Possible turn 2 delays: 1 1 1, 1 1 1, 1 1 1, 1 1 1
Damage taken on turn two: 20970
To plan your HP accordingly... Apart from the boss... the highest damage you will take on any turn is on round 3 ( 1 king, 2 highs) for 25500 so I would take that as the minimum HP requirement for entry. In order to activate 25x you need to have less than 20% HP. (5099HP for 25501 team HP)
I see certain HP levels as being better than others...
34950+ is the most I would bother to bring for goemon setup
27960+ is minimum to survive full attack during round 1
25500+ is minimum to survive one attack during round 3...
20970+ is minimum to survive worst case attack turn 1 round 1
Its still a crapshoot on what your starting round and board looks like... but bringing 27960+ HP team allows for the least healing with the highest chance of activating 25x... 37.5% chance to activate 25x without doing anything on turn 1 and 2 . 37.5% chance to activate 25x after turn 2 while healing approximately 6990HP on turn 2. And finally a 12.5% chance to activate 25x after turn 2 or 3 by healing 13980HP (not realistically possible).
Edit: 4 high dragons to start...
Possible turn 1 delays: 2 2 2 2, 2 2 2 1, 2 2 1 1, 2 1 1 1, 1 1 1 1
Damage taken on turn one(percent chance to occur): 0 (7.1%), 6990(28.5%), 13980(28.5%), 20970(28.5%), 27960 (7.1%)
Possible turn 2 delays: 1 1 1 1
Damage taken on turn two: *27960
With 25x dmg, you just need to make sure to get over 4000base dmg (Assuming a 6 combo turn, just need 2 3gem of your target color to break their defense and kill them) 2000 base dmg if color weakness.