user33320: I had an Arduino UNO (ATmega168) standalone working, but I need more pins, and I decided to use the ATmega2560, I was searching for some schematics, and none of them shown an ATmega2560 standalone, only the full Arduino, with the FTDI, power transformers... etc integrated. So taking parts from those designs, I made this, but I don't know if it's enough or I need Something more:

Note: VCC2 is connected to 5V.

user30005: 
check the datasheet;
I would put a pull-up on the reset pin, plus a small capacitor;
crystal + capacitors as optional;
AVCC to VCC with filtering, if you need good analog performance;
separate Vbat domain, if it has one.

...

user4143: You need more decoupling capacitors - one per VCC and AVCC pin, plus a larger (10µF) for the whole chip.
You need a pullup resistor (and maybe button) on RESET.

33320: <p>I had an Arduino UNO (ATmega168) standalone working, but I need more pins, and I decided to use the ATmega2560, I was searching for some schematics, and none of them shown an ATmega2560 standalone, only the full Arduino, with the FTDI, power transformers... etc integrated. So taking parts from those designs, I made this, but I don't know if it's enough or I need Something more:
<a href="https://i.stack.imgur.com/eQ5n1.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/eQ5n1.png" alt="enter image description here"></a></p>

<p>Note: VCC2 is connected to 5V.</p>
 30005: <ol>
<li><p>check the datasheet;</p></li>
<li><p>I would put a pull-up on the reset pin, plus a small capacitor;</p></li>
<li><p>crystal + capacitors as optional;</p></li>
<li><p>AVCC to VCC with filtering, if you need good analog performance;</p></li>
<li><p>separate Vbat domain, if it has one.</p></li>
</ol>

<p>...</p>
 4143: <p>You need more decoupling capacitors - one per VCC and AVCC pin, plus a larger (10µF) for the whole chip.</p>

<p>You need a pullup resistor (and maybe button) on RESET.</p>
