Core Cannon 
Feat 17
Source Pathfinder Guns & Gears
Frequency once per day
Your body transforms into a powerful magical cannon. While immobile as a cannon, you can fire blasts of energy directly from your core, devastating your foes. You become Immobilized until you use an Interact action to revert back to your standard form. While in your cannon form, the only actions you can use are to Strike with an energy blast unarmed attack or to Interact to revert back to your standard form. You can remain in your cannon form for up to 1 minute or until you take the action to revert back to your standard form, whichever comes first.
Energy blasts are a special ranged unarmed attack. You can only make energy blast Strikes while you're in your cannon form. Your energy blasts deal 3d8 fire damage and 3d6 force damage, which increases to 4d8 fire damage and 3d6 force damage at level 20. You gain the item bonus to attack rolls with your energy blasts from the highest potency rune on any Handwraps of Mighty Blows you are wearing or any weapon you are wielding, but striking and property runes have no effect on your energy blasts. Energy blasts have a range increment of 120 feet. On a critical hit with an energy blast, the target takes 10 persistent fire damage. Your energy blast doesn't add critical specialization effects. If it matters for an effect dependent on weapon damage dice, an energy blast's number of weapon damage is three, or four at level 20.
Effect: Core Cannon
Traits
Anything that doesn't list another rarity trait (uncommon, rare, or unique) automatically has the common trait. This rarity indicates that an ability, item, or spell is available to all players who meet the prerequisites for it. A creature of this rarity is generally known and can be summoned with the appropriate summon spell.
ArcaneThis magic comes from the arcane tradition, which is built on logic and rationality. Anything with this trait is magical.
AutomatonA creature with this trait is a member of the automaton ancestry.
ConcentrateAn action with this trait requires a degree of mental concentration and discipline.
PolymorphThese effects transform the target into a new form. A target can't be under the effect of more than one polymorph effect at a time. If it comes under the effect of a second polymorph effect, the second polymorph effect attempts to counteract the first. If it succeeds, it takes effect, and if it fails, the spell has no effect on that target. Any Strikes specifically granted by a polymorph effect are magical. Unless otherwise stated, polymorph spells don't allow the target to take on the appearance of a specific individual creature, but rather just a generic creature of a general type or ancestry. If you take on a battle form with a polymorph spell, the special statistics can be adjusted only by circumstance bonuses, status bonuses, and penalties. Unless otherwise noted, the battle form prevents you from casting spells, speaking, and using most manipulate actions that require hands. (If there's doubt about whether you can use an action, the GM decides.) Your gear is absorbed into you; the constant abilities of your gear still function, but you can't activate any items.
TransmutationEffects and magic items with this trait are associated with the transmutation school of magic, typically changing something's form.