Protection from a color, as seen on LEAs Ward cycle (including Green Ward), is the most common form of protection, but you can also get protection from creatures (Spirit Mantle), protection from player(s) (The One Ring), and even protection from everything (Progenitus)
There are at least 10-15 cards I didnt mention, so feel free to mention them in the comments
If Kaalia attacks an opponent, the creature enters attacking that player even if Kaalia is somehow attacking a different player or planeswalker as its triggered ability resolves
Delirium - Whenever this creature attacks for the first time each turn, if there are four or more card types among cards in your graveyard, untap target creature
Volo, Guide to Monsters, is the MTG embodiment of the term variety is the spice of life. Theyre a four mana Green and Blue 3/2 that reads, Whenever you cast a creature spell that doesnt share a creature type with a creature you control or a creature card in your graveyard, copy that spell. Were all about getting value out of our cards, and getting an extra copy of every Creature you cast is the kind of thing you cant help but enjoy.
The condition of a card is also important