#1 - (PHB 266) The number of times that you can use any daily power granted by any magic item is limited by the PC level. You CAN use more than one magic item daily power per day at Heroic Tier. The catch? You have to reach a milestone first.
#2 - (PHB 277) The effect of a monster marking a target is not described in the books, but the condition is. –2 attack if the marked target attacks anyone other the the monster that marks it.
#3 - (PHB 59) Powers with a hit that also have an effect still get the benefit of their effect even if the power misses. As the DM I didn't give some of my players the benefit from their attacks.
#4 - (PHB 267) No Action points can be used during Surprise rounds.
#5 - (PHB 60, and in the first page description of each character class) The starting HP of a character is their Class HP + their CON score, not their CON modifier. This is the most common 'oversight' I saw in players who've played 3.x before.
#6 - (PHB 208) The class-specific multiclass feats qualify you to take paragon paths from that class only if you have the prerequisites necessary for that particular path.
#7 - (PHB 287-288) Charge is a standard action, so you can still take a move action in the same round. However, using a charge ends your turn, so you can only move before you charge.
#8 - (PHB 201) Toughness feat only gives +5 HP At each tier.
#9 - (PHB 263) You can only take an extended rest once every 18 hours (Or every 12 hours if you don’t add in the time spent during an extended rest, but let’s not bring that one up again). Seemed fishy after my parties third extended rest in the 5th room of a dungeon
#10 - There are no more Full Round Actions, get over it.
#12 - (PHB 295) When you subject to a healing effect that requires you to spend a healing surge and you have none left, you are restored to 1 hit point, if you were dying.
#12 - This is not D&D 3.75.
#14 - (PHB 268) The limits on immediate actions and the difference between immediate and opportunity actions.
#18 - (PHB 294) Temp hp don't make you conscious -- if you are at 0 (or less) and receive Temp hp, you are still unconscious. Came up during a game with a Warlock exactly on 0 and receiving 1 Temp hp from pact boon (GM ruled okay, but I looked it up later).
#19 - (PHB 295) When you reduce a monster to 0 hp you get to choose if you either knock it unconscious or kill it. (i.e. instead of nonlethal damage).
#20 - (PHB 291) Ready an action is an Immediate Reaction (occurs after, one immediate per turn), although your initiative is set to immediately before the creature that triggered. (Both Ready and Delay are largely similar to 3.x, however I played some games where the GM ran it diferently).
#21 - Two-handed weapon now probably means only the category, not how you wield it, e.g. for power attack. This is the reverse of 3.x, where how you wielded it was generally important. This comes into play when using a versatile weapon. If a power or condition requires a two-handed weapon it refers to the category of it, not how it's used.
#22 - (PHB 30) Defenses add 1/2 level, and so AC automatically goes up.
------------------------------------
#22 - (PHB 62/90) clerics and pals don't need to wield their implements like wizards etc. They can just hang them round their neck. Cue the party cleric swapping quick draw for shield proficiency!
#23 - (PHB 195) expanded spellbook feat gives you an extra daily but not an extra utility per level. Cue disappointed wizard pc..never assume check
#24 - (PHB 214) When using a light shield, one is able to hold items,load a hand crossbow and even climb and still use it. Sounds like that sword arm may not be limited to only holding a torch or sunrod.
#25 - (PHB 285) You do not need to hold a weapon in order to obtain combat advantage through a flank. You can be armed or unarmed.
#25 - (PHB 56) You don't need an implement just to use a power with the Implement keyword, regardless of your class. Not having an implement has no ill effects, apart from Wizards losing the benefits of Arcane Implement Mastery.
#27 - (PHB 198) Int 13 is a pre-requisite for Linguist. If you don't have Int 13, there is no way (that I can see) to learn additional languages.
#28 - Most big creatures (including dragons and such) do *not* have threatening reach... meaning no AO's unless you are adjacent to them.
#29 - (PHB 285) You can flank, and even gain combat advantage for attacks, with a ranged weapon (or any attack). You still need to be adjacent to the target (so usually making the ranged or area attack would provoke), but still useful to know if there is something you really, really need CA for with a ranged or area attack.
#30 - (PHB 105) Did you know that Twin strike damage does not get modified by any abilities i.e. STR or DEX
#31 - (DMG 38) Like monsters can ready within their own turn in order to wait for another monster to get into a flanking position. This is relevant when you have something like 2 or more same monsters attacking using the same initiative.
#32 - (PHB 40/195/286) Did you know that an elf PC with Fast runner feat and using his Action point can Run 33 squares in one round. (Ok, it was determined that an elf can move even more then this, but you get the picture)
#33 - (PHB 294) Temporary hit points don't stack.
#34 - (PHB 268) You can only use an Immediate Interrupt or Reaction once per Round, not both.
#35 - (PHB 268) You can not use an Immediate Interrupt (A more accurate statement would be Immediate ACTION) on your own turn.
#36 - (PHB 61) You can only use one Channel Divinity power during an encounter, regardless of how many you know.
#37 - (PHB 198) The Human perservances also adds to death saving throws.
#38 - (DMG 44) You get a saving throw to avoid being forced movement into hindering terrain. This leaves the target prone at the edge of their current square.
#39 - (PHB 290) You don't move into your opponent's square when you grab. Even if you're a stirge. In fact, I don't think you ever share a square with an opponent any more for any reason. Gelatinous Cube and Shambling Mound is one exception to this.
#42 - (PHB 291) Monsters can't take Second Wind unless the description says they can.
#43 - (PHB 210)Starting gold is 100g
#44 - (DMG page 143)Starting wealth rules for PCs above first level.
#45 - (PHB 292)Standing up from prone no longer provokes attacks of opportunity.
#46 - (PHB 289)Drinking a potion as a minor action.
#47 - (PHB 289)Also, it's a standard action to equip a shield
#48 (PHB 278) Sneak attack maxed on a crit.
#49 - (PHB 263) There is a penalty for not taking an extended rest. You need at least 6 hours of sleep every day to keep functioning at your best. If, at the end of an extended rest, you haven’t slept at least 6 hours in the last 24, you gain no benefit from that extended rest.
#50 - (PHB 285)If you’re affected by an effect that prevents you from taking opportunity actions, you don’t flank.
#51 - (PHB 290) Close Blast or Close Burst do not have the keyword "Ranged" or "Area" and as such do not provoke OA.
#52 - (PHB 290) You can make an OA once on each other creatures turn, but you can make any number during the round.
#53 - (PHB 212) You don't add your dexterity bonus to ac if you wear anything other than light armour, but you have a choice between DEX and INT for light armor AC bonus.
#54 - (PHB 209) You couldn't use a power-swap feat on a power from your Paragon Path or Epic Destiny.
#55 - (PHB 76) When a fighters Combat Challenge is trigged due to a marked, adjacent enemy shifting, the shift is not interrupted. It's just that the triggered action (melee basic attack by the fighter) occurs before the shift is completed.
#56 - (PHB 295) You can only fail 3 Death Saving Throws TOTAL between short (or extended) rests. So if you go down, fail 2, get back up, go down again, and fail 1, you are D-E-D, dead.
#57 - Healing affects you differently when you are "dying". If you are Healed while dying, your negative Hit Points are reset to 0 before you gain Hit Points form the Healing Effect. If the Healing Effect requires you to use a Healing Surge and you have none left, your Hit Points are instead set to 1 HP. Temporary hit points don't cause you to stop dying.
#58 - (PHB 287)(Number your rules, demmit) With a reach weapon, you can make a charge attack and do NOT have to end the move adjacent to the charged enemy. "You must move at least 2 squares from your starting position, and must move directly to the nearest square FROM WHICH YOU CAN ATTACK YOUR ENEMY. You can't charge if the nearest square is occupied. Moving over difficult terrain costs extra squares of movement as normal."
#59 - (PHB 217) Even with a reach weapon, enemies do no provoke opportunity attacks unless they are adjacent to you.
#60 - () Only three things draw an OA: A non-shift move out of a threatened square, using a Ranged or Area power in a threatened square, or when it specifically created by way of a power.