This is my first judge posting on this forum, so please bear with me!

A situation arose at our most recent FNM sparking my first ever time using the penalties feature in event reporter. It was modern, and Alvin attacked with a bevy of artifact creatures including an arcbound ravager. Niles is tapped out and assembled his blocks in a way that he was taking non-lethal damage. Alvin passed priority as he had no intention of sacrificing anything to Ravager (he is newer to modern and has not played the deck much).

At this time, a spectator pointed out that Alvin could sacrifice artifacts to Arcbound ravager and then the ravager himself onto a flier to present lethal damage. Assuming that Alvin and the spectator have never met, what, if any, penalties should be given at Regular REL?

No penalties. Have a chat to the spectator that providing that sort of assistance isn't very fair, and please ask them to refrain in the future.

There's no penalty I'd asses in this situation. Regular REL basically has two level of penalties, as it's meant to be an introductory level of competitive play; either I tell the offender that that's not a good thing to be doing, and explain why, or I disqualify the offender(s) for cheating or collusion. There's no middle ground.

I've only once assessed a different penalty a a match loss for tardiness - and that was discussed with the participant before he left the venue due to an emergency.

Let's take a close look at the JAR! Under General Unwanted Behaviors, the third bullet point mentions “Asking for or providing strategic advice during a match or draft.” That's exactly what happened here. The remedy? "As a judge, the priority is to educate players who exhibit these behaviors. It can be useful to reinforce this education with more stern penalties such as a Game Loss should the unwanted behaviour continue.“

At Regular REL, we usually only educate or disqualify a player, there is no real middle ground, as Tim already pointed out. If the spectator continues to interfere with matches being played by providing strategic advice, you could hand out a Game Loss. But it is extremely rare for this to actually happen.

On a side note, you mentioned the ”penalties feature in event reporter". This is mainly there because we also use WER for Competitve REL events. Penalties and software are not linked at all… we just don't really do penalties at Regular REL, even when we use WER. In case you have to hand out a Game Loss or other penalty, your first priority is to clearly communicate this to the player and educate them; entering the penalty in the software is of secondary importance (entering a DQ in the Judge Center however is extremely important!).
Make sure you are entered as a judge in the Event tab, click the penalty tab in WER, and select all appropriate items from the drop down menu. Because there are no Warnings at Regular REL, I recommend using terminology from the IPG to select the most appropriate infraction. Don't worry too much about this.