These were found via the NewRelic API and don't seem to be documented anywhere. They seem to reset automatically at midnight, so its possible to create NR alerts for blocks if needed.
Note that the plugin on NewRelic hasn't been updated in a while as of the time of this writing; clicking the button to install it will yield a 404. However, configuring it from the Sendgrid side will cause the data to be send and start appearing in NR.
Component/Numeric/Compliance/Blocked[Emails/Day]
Component/Numeric/Compliance/Bounces[Emails/Day]
Component/Numeric/Compliance/Spamreports[Emails/Day]
Component/Numeric/Deliveries/Deferrals[Emails/Day]
Component/Numeric/Deliveries/Delivered[Emails/Day]
Component/Numeric/Deliveries/Drops[Emails/Day]
Component/Numeric/Deliveries/Requests[Emails/Day]
Component/Numeric/Engagement/Clicks[Clicks/Day]
Component/Numeric/Engagement/Opens[Opens/Day]
Component/Numeric/Engagement/Unique-opens[Opens/Day]
Component/Numeric/Engagement/Unsubscribes[Unsubscribes/Day]
Component/Percent/Compliance/Blocked[Percent]
Component/Percent/Compliance/Bounces[Percent]
Component/Percent/Compliance/Spamreports[Percent]
Component/Percent/Deliveries/Deferrals[Percent]
Component/Percent/Deliveries/Delivered[Percent]
Component/Percent/Deliveries/Drops[Percent]
Component/Percent/Deliveries/Requests[Percent]
Component/Percent/Engagement/Clicks[Percent]
Component/Percent/Engagement/Opens[Percent]
Component/Percent/Engagement/Unique-opens[Percent]
Component/Percent/Engagement/Unsubscribes[Percent]