This guide will show you to create a batman pumpkin illuminated by LEDs in a small form factor.
CR2032 Lithium 3V batteries
Carve the pumpkin with any design. I chose a Batman Symbol.
Make sure to use a current limiting resistor so you do not burn out the LEDS. Calculate the resistor value using ohm's law V=IR, mine turned out to be an 8.7 ohm resistor to get about 24mA of current (max for these super-bright LEDs).
Solder the negative contacts of the LEDs to a small resistor.
Wrap the positive contacts of the LEDs to the positive lead of the battery with electrical tape. Bend the resistor and LEDs such that the LEDs point radially outward, and the resistor can be tucked under the electrical tape (creating a removable switch to turn off the LEDs).