These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Game Breaker: Thermite the thermonuclear termite is basically all you need in the game after you acquire him (to be fair, he's the last warrior you get.) He can also shoot napalm and an upgrade lets him shoot trolls, which for some reason explode.
Ash and Thermite are healed by fire. Spend 3 Elemental fruit for Ash's "Incinerator", and stand in it to Heal Thyself without boxes.
Deep Blue's water jets are very adept at knocking enemies into pits and water, which is instant death for them. It's also a great way to get combo points.