1) Weapon Arts - (Unless Edited) Press L2 to perform the main hand / off hand weapons Weapon Art.
2) Estus Chugging - Mash the Use Item button to continuously chug it.
3) Ladder Battle Mechanics - You can punch upward or kick downward to attack enemies while climbing ladders (Either R1 or R2 forgot what the kick and punch is). being hit with this drains stamina. drain their stamina and the will fall the ladder.
4) Ladder Estus Chugging - Well, you can chug that estus while climbing.
5) Summoning - Has 30 Seconds Cooldown per summon (I haven't tried it, anyone confirm?)
6) Phantom difficulty - The more friendly phantoms you have, the more the enemies HP adjusts
7) Password Summoning Scale Down - If the character being summoned is much much overpowered compared to the host, the phantom would be scaled down to close to the level of the Host.
8) Purple Summon Signs - summons Mad Spirit, It's on their own decision if he will help or kill the host. (common knowledge, but helpful for starters who doesn't know this as this covenant is kinda hidden)
9) Frost Status Effect - Increase damage and slows stamina regen if inflicted. When proced, will deal 10% HP damage, you can remove frost effect with any fire based damage.
10) Curse Status Effect - Insta kills you if the built up finished
11) Being Embered - it makes you open for Invasion that means PvP. (some are NPC but surely most of the time it's Players, sometimes, name hint's if it's a player)
12) Location Population - during location pick on bonfire, you will see an icon (don't know what that is) that means it has more population at that area in range of your SL and weapon upgrade. more icons = more people.
Edit 1 as added by itztaytay (also edited the others on top as he clarifies some of them):
1) 2 Handing Weapons - Performs stronger attack or more stability to shield while 2 handed, some weapons are special in which you will be equipping two types of weapons or shield instead. Press (unless edited) "Triangle" or "Y" button for main hand 2 hand and hold down the button for off hand 2 hand.
2) Torch - Removes leeches. certain enemies apply leeches to your character that builds bleed status on a long duration (about 2 or 3 bleed procs based on experience) equip a torch to remove them.
3) Dried Fingers - a special item for you to increase number of friendly summons by 1, but increase the chances of invaders and its maximum number by 1.
4) Quick Item / Magic Switch - Hold down the switch Item / switch Magic button to switch the selection to the first equiped item / magic
5) All statuses have Hp scaling (Frost, Bleed, Poison, Toxic, Curse) and is the ONLY way they scale. Increasing buildup will let you proc the effect faster but does not change the damage at all, only the enemy's max Hp does that. (also storyteller staff is way better than normal poison for some reason)
Edit 2 as added by Emad-520 (Some of his contributions are edited above, others are bellow):
1) Dying as an Invader - If you die during invasion, it drops your souls on the location of your death.
2) Being Blue Phantoms - Killing players with the covenant "Watchdogs of Farron" and "Aldrich Faithfuls" won't give you rewards.
1) Poise - the ability to withstand an attack. only works on certain type of weapons during attack. (correct me here)
2) Hollowing Level - is increased everytime you die, the number of increase is based on the number of dark sigils on your inventory
3) Alluring skulls works on NPC invaders
4) Ladder Jump - tap the run button twice.