The Morning Stars familiars need to charge a "Starchild" to attack, they can charge up to 5 of them, but for some weird reason, even if you have 5 stocked, you can still use the "Gather Starchild" command, this means that you will loose 10 mana and won't receive anything in exchange. So, be sure not to "click" the "Gather Starchild" command more of the necessary or you will be wasting mana.
If you are fighting against Astral familiars, you can send a Chimera and a Homunculi against them. This may sound stupid at first, but by using the "Clairvoyance" skill of the Homunculi on the ghosts enemies, you'll be able to inflict physical damage to them, this means that your Chimera will be able to kill them with its attacks. And since the Chimera has a really high attack power and mobility, these two will be almost unstoppable against ghosts.
Blobs, Homunculi and Grimalkins may appear to be weak familiars, but if they are used properly they can serve for various purposes during battle.
Grimalkins can put to sleep all big and powerful foes, if you are being attack by a Dragon or a Chimera you can make the Grimalkins put them to sleep and attack them while they can't defend themselves. Also if you level up the rune, they will obtain the skill "Mana Burn" which will allow you to easily kill enemies with MP using the Grimalkins.
Homunculi can turn Astral enemies into physical beings allowing you to damage them with physical attacks. If you level up the Rune until you acquire the "Physic storm" ability for the Homunculi you can also use them for defense, since they can summon a storm wherever you ask to. If you make Homunculi to summon a storm in one spot of the map (let's say where the attacking enemy army is) it will cause big damage.
Blobs can slow down enemies, while not as useful as the other ones, it does help when you are being attacked by a big enemy army. Just keep in mind, that you have to level up the "Laboratory" rune in order for your blobs to be able to use that ability.
In every mission the game will offer you a hint if you re-start the mission. So if you aren't sure what you should do to improve your chances of winning against the enemy and/or you are loosing, open the menu by pressing start and re-start the mission. The game will then give you a hint regarding on how to win, before dictating the winning conditions of the mission.
In order to unlock the "hard" difficulty setting, you have to complete all the story-line missions and extra missions in the "normal" difficulty setting.