I just played my first game ever against my friend but as we are both new, we were a little confused by his Sentry’s trait of VOID.

We are pretty much confused about everything for this Sentry.

It says +5 points. If we are to build around Sentry does this mean he will ALWAYS have his original point value plus 5 anytime he’s played in a game? What exactly is this VOID trait?

It says we can replace Sentry with his prime version however since he is a prime, if the team already had a prime on the team, would this be allowed since 2 primes would be on the board?

The +5 is an optional trait. You do not need to opt to use it, but if you do it would cost 5 points to add it to your force.

You could not replace Sentry with his prime version if you already have a prime on your force. You can only have 1 prime character on your force, which includes your sideline, which is where replacement characters come from.

See sections 2.2, 2.4b and 2.6 in the Comprehensive Rulebook linked below for the official rules on all of this:

https://wizkids.com/posters/reposito....22.pdf#page18

As a new player, it's also worth noting that the point costs on Sentry's card and dial do not match up. I'm not sure if this is part of what was confusing you, but either way note that it is an error. Wizkids has clarified that Sentry is supposed to cost 115 points, so 120 if you want to bring in the Prime version.

https://www.hcrealms.com/forum/showthread.php?t=842331