This will make everyone think Herobrine has joined the game, and it will blame a random player. If you want it to blame a specific player, edit command block 2 and replace @r with the desired blame player's username.
These are different commands, so just copy/paste them from here (without the numbers at start). The actual command box only had the join command.
1. /tellraw @a {"text":"Herobrine joined the game.","color":"yellow"}
2. /tellraw @a {"text":"<Herobrine> So, @r you allowed me to join?"}
3. /tellraw @a {"text":"Big Mistake","color":"dark_red"}
4. /tellraw @a {"text":"imherobrineandyoushallrecivemywrath","color":"dark_green","obfuscated":"true"}
5. /tellraw @a {"text":"Herobrine left the game.","color":"yellow"}
Step 1: Put blocks 1, 2, 3, & 5 in a straight line one block apart from each other.
Step 2: Place command block 4 two blocks behind command block 3.
Step 3: Connect blocks 3 & 4 with two peices of redstone.
Step 4: Put buttons on every command block exept 4.
Step 5: Activate the command blocks in order, 3 & 4 will go at the same time.