Different in the description of Pentagram means that you do not get 2 mana for attacking and damaging the same creature twice. If you want to get the second mana, you'll need to attack and damage another enemy creature.
When casting a spell with a spawnpoint, the mana comes first from the spawnpoint, and then from your mage. So if you have 3 mana on Pentagram and you want to play Dark Pact Slayer, the first 3 mana comes from the Pentagram, and the remaining 10 mana comes from your mage.
Suppression Cloak makes it cost mana to attack your mage for each creature attacking you. So if I have 4 Timber Wolves in the same zone as your mage, and you have Suppression Cloak equipped, I will need to pay 2 mana for each Timber Wolf when they attack you for a total of 8 mana to make those 4 attacks.
