Start with bubble. whirlpool when ready, otherwise spirit claws
When dead switch to spawn and dive before the cannon. Thunderbolt and finish with Swallow
If spawn can't make it finish him with last pet
This (kind of) worked the second time for me (I got unlucky with RNG the first time.
The moves from Spawn don’t make a lot of sense to me (at least the first option), and I had to add in a Thunderbolt as those moves didn’t kill Pilfer. I think the first move options are mixed up - should be Thunderbolt if Pilfer has >538, not <538.
Didn't have Slithershock Elver level'ed - Replaced with Gulp Froglet 1/2/2
Puddle Terror in
Water Jet until your Puddle Terror dies (If you get crit once - Restart fight)
Gulp Froglet in
Spawn of G'nathus in
Swallow You Whole
Puddle terror is a must first off as you get two free hits at him - use the strategy listed - if die before next 2500k attack then wipe and restart - if you are alive usually with 3 health then carry on and next big attack kills you- use slivershock elver with dodge and spawn of gnathius with dive and you should be good as long as puddle terror was the one to die on his second big attack - don't be afraid to swap in a pet too handle his massive attack you have dodge and dive
Puddle terror 1-2-2
Spawn of Gn.athus 1-1-1
Slivershock elder 2-1-2
Puddle Terror P/S level 24 followed above strat, second pet was a 25 Rare P/S Mongoose with Gnaw survival and dive, Spawn of G'nathus finished the fight. If you try to replicate watch when to use Survival to get in a last Gnaw before it dies. Done with Pilfer, again thanks for this site.
This worked and as long as Puddle gets killed by the massive attack, the order for the Mongoose is Gnaw, Gnaw, Dive, Survival, Dive, Dive, then you die, in comes G'nathus, and dive, thunderbolt, blood in waterx2 and barely win.
Since my Slithershock Elver is only L3, I used this strategy with a P/S Mongoose Pup and the tweak of Spawn casting Dive on his first turn. The way my battle worked out, he has to do that or he dies immediately. Thanks to everyone for the great strategies and tweaks.