I’ve been level 150 for a long time, theory to me for ~ the past 2 years that these breeding hearts and hatching hearts have become much harder to achieve, which is similar to war becoming more rigged (they dodge 30%, i dodge 5%), war opponents (computer bots) are obviously given more agility and accuracy...more deception to the player. Regardless my theory for high levels is to breed two breeds off any type , then breed one more 31+ second breed after 8 hours before last heart, if I breed 2 legends In a row I get no heart , if I breed 30 pandaken after the two legend I get no heart.

Try just breeding x2 Pandaken, it's either 30sec or 15 sec to breed and gets hearts/eggs (when off CD). Works 100% for me.

@lezter-wiel-garin don't know if you meant to post it in Monster Legends or DC but don't think someone is going to give you that. You have to grind for it. If it's DC please go to DC section