Your Princes and Princesses have +2/+2 for each Prince and Princess you’ve Upgraded.
The wording on the card is a little unclear. The boost refers to every Prince or Princess you’ve upgraded throughout the current game. You don’t have to have made the upgrades on the current turn, nor do you need the upgraded characters in your current squad. So if you’ve upgraded two Princes and one Princess earlier in the game, every Prince/Princess in your squad gets a +6/+6 buff.
Comps, Combos and Synergies
One good thing about Mihri is that you don’t need to worry about the best build. If you’re playing Mihri, you’re going for Prince/Princesses. The usual aim is to have upgraded Juliet(s) in the front row, upgraded Romeo(s) in the back and Prince Arthur buffing them every brawl. Along the way to this combo, you’ll want to be upgrading minor Princes and Princesses then probably swapping them out.
If you’re not playing Mihri but one of your opponents is, you might want to think twice about going for a Prince/Princess build: you know you’ll be competing against Mihri for the limited number of characters in the shared pool. But you might still like to buy a Romeo/Juliet/Arthur or two just to make life more difficult for Mihri.
Game Update History
Patch 62.3, September 2021: Moved to standard Advanced Hero pool instead of being restricted to slot 4
Early Access Patch 61.1: First introduced
List Of Heroes