- Every time Mario and Luigi share a hug when they meet after being separated.
- Also deserving of mention is their hugging Princess Peach after she is kidnapped in Teehee Valley (which you can repeat, even multiple times, if you let her get captured again). There's no unique sprite, so it's staged as just the Mario-&-Luigi-hugging sprite over top of Peach's, but it gives the impression of a Group Hug, which is very touching as it really shows how much the plumbers and princess appreciate each other's company and help.
- When either one of the brothers suffers a KO in battle, the one still standing gets an absolutely horrified expression, rushing over to the fallen one and supporting his unconscious body.
Heartwarming / Mario & Luigi: Superstar Saga
Note: Minion Quest: The Search for Bowser examples go here.