Romance

Well, it depends on which one is male and which one is female.

They will breed an egg, and the Pokemon that is in the egg depends on which parent was the female; if the Pikachu is female, then the result from that egg will be a Pikachu. Or, if the Monferno is female, then the result from that egg will be a Chimchar.

Or are you checking the Friendship Checker? Because that's the relationship between the pokemon and YOU.

The two pokemon also need to be a part of the same egg group, which does apply to Pikachu and Monferno. The two pokemon also need to be of opposite genders; two female or two male pokemon would not cooperate; the two pokemon need to be MALE and FEMALE.

It's probably just a glitch in your game. Save your game and try it then check if it crashes your game restart it.

Your 'love checker' isn't how much your Pokemon love eachother, it's how much they love, or are friendly to you.

Pokemon breeding has a lot to do with the pokemon's Breeding Egg-category. Which has nothing to do with it's nature (Quirky, Lax, Jolly etc.) or it's type (Water, Normal, Psychic) Pokemon are also categorized into Breeding types such as Fairy, Human-shape, Monster etc. Which define the types of Pokemon that it can breed with. Some can cross egg-categories for breeding. So just try anyway.

Monferno is Human-shape and Pikachu is Fairy type. You chances are, tya will not breed with eachother. You will be able to tell, if the daycare man says "they seem to get along" they will breed, or "they don't seem to like eachother" they wont breed.

If you want another chimchar, migrate a Ditto to your Diamond game, and breed with monferno. You will get a chimchar.

Whan breeding Pokemon, you usually have a mother or father. They don't have to be both, say Zigzagoons, but that will guarantee you another zigzagoon. Say you had a jigglypuff and a clefairy. (both fairy type) If the mother is a jigglypuff and the father is a clefairy, you will get a baby jigglypuff. The baby is always what the mother Pokemon is. (that is likely why most people's starter Pokemon are male.)

If you breed with a genderless ditto, however, ditto will breed with anything that can breed (no legendaries, except for Manaphy) and even if it breeds with a male Pokemon, you will get a pre-evolved version of whatever you breed with Ditto. Want a Bulbasaur but you only have a male, breed it with ditto, and you'll have one! Fantastic, Isn't it?

Essentially nothing that is interesting at all. They are not in the same breeding group so they are not capable of producing an egg. Essentially all that will happen is that they will go up levels like every other Pokemon does who is in the day care.

It depends if it's a female infernape and a male pikachu youll get a chimchar if it's a femal pikachu and a male infernape youll get a pichu. This is of course as long as they like each other

They would just levle up

No eggs sorry

Scotland23

That has othing to do with how much they like eachother, it means how much they like you.
If you put them in the daycare center, othing happens, they just get EXP.