Not a fast strategy, but it allows for a level pet with low health requirements (Beast: 664HP, non-Beast: 443HP, Elemental: 295HP).
Works with a P/P Blazehound. With a S/B you likely have to add one Bite after the second Puppies with Corporal, and the RNG risk (see below) is higher.
RNG with Clamp:
It can happen that Squashling is still rooted by Clamp where the description says “release Plant”. Haven’t seen this in a while, but it can happen. We are screwed then. Low prob.
RNG with Blazehound:
The non-crit damage of Obsidian Bite varies between 379 and 705. So, if you are unlucky it may happen that your Blazehound doesn’t bring M-37 into Failsafe. In that case you have two choices: 1) If the leveler XP is important, then restart the fight. 2) If not, then bring in your Squashling (instead of the leveler) after Blazehound’s death: You will then win the fight, but your Squashling may survive and you won’t get XP.
Not every strategy can be bullet proof. This is one of them. You might have to restart it, since there are some random elements that increase the risk of your pets failing. Don't blame them, please!
You can use this strategy to carry a level 1 level pet to give it experience.