Watch out for....
As you may or may not have noticed, the rival events happen more frequently than on FOMT or MFOMT. So to prevent this, I think that you should try to give the girl you like before the rival is in the same place as her. Lucky for you I will list all the rivals.
Muffy's Rival is Griffin
Celia's Rival is Marlin
Nami's Rival is Gustafa
Flora's Rival is Carter
Lumina's Rival is Rock
Also if you do manage to get them in the same place, if you haven't seen any other rival events, do not catch:
Do not catch Nami and Gustafa at the pond by Cody's
Do not catch Lumina and Rock at the Goddess Pond
The rest of these are somewhat easy to trigger accidentaly, as they often are in the same place
Muffy and Griffin at the bar
Celia and Marlin at the seed shop with Vesta
Flora and Carter at the digsite
Lord that was a lot of typing!
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