Well, I have max strength, blade, hand to hand, and sneak, but still cannot kill most sleeping victims in one shot. It was fairly easy at lower levels but now, since I'm level 45 it seems my ability to assassinate has disapeared.

Any tricks or tips to be able to assassinate once again?

Yea, it gets harder as you level due to level-scaling.

Luckily for you, His Holiness has chanced upon this thread and shall shed some light on the matter.

First off, you're going to need to work on Alchemy. Make some potent poisons. If you can't/don't want to make them, buy them. They're necessary.

Second of all, make sure you're in sneak mode, as that gives you a multiplier bonus.

Third, make sure to use some powerful enchanted weaponry for the one-shot kills.

Lastly, if all else fails; lower the difficulty slider.

Good Luck. The Holy Assassin walks with you.

That is one of the reasons why I rarely take a character past level 30- it is just giving HP to the enemy.

Holy Assassin is right about poisons, also make sure that your blade enchantment is the best you can make. Greater souls baby!!
The blade must also be single handed, otherwise you dont get the highest multiplier.

It is a shame that we dont have the Sandman perk from Fallout....

Yeah, thing is with custom potions and enchants, you cannot get them to be instant. The lowest you can get is 1 second, which still gives them time to kill a guard. Unless there's something I can fortify to increase my damage substantially for a single blow, then I do believe I might have overleveled this turd.

If you use Deadly reflex mod, you will instakill any sleeping enemy with a four stabbing animation. I had only try 5th version yet, but surely the 6th one will also have this feature.

If you didn't want to use this mod, you can yet use Oblivion Elys uncapper. This mod let attributes and skill affect damage until 200. This way you can use strength and weapon skill increasing effects, even if you had reached 100 in them.

Also you can use in the poison and magic combo a paralysing effect. This way the enemy won’t be able to fight, while the other non instant effect are killing them.

You can reduce your level via console with player.setlevel number. And this is not cheating, nor crippling your character, as your hard earned experience has been weakening him lately.

For future characters, you should consider using mods like FCOM or TIE to make the enemies unlevelled. This will make the game way more exciting at lower levels and as I see by your experience less annoying at higher ones.

I fear that you may have overleveled also. You want your victims with as few hitpoints as possible.

One hit instakillers should be groomed from an early age to work hard at getting the following things in order at a reasonably low level - perhaps 20, but certainly no higher than 30:

100 strength (damage)
100 blade (damage)
75 armorer (125% repair = more damage)
100 sneak (although you get 6x damage at a skill level of 25, you want 100 so you can ignore your victim's armor rating)

Add a very strong base damage one-handed weapon (such as Umbra or a daedric longsword). You can get Umbra at any level. Daedric long sword takes level 20.

Remember that self-enchanted weapons deliver their enchanted damage over at least 1 full second - that is not instant and it can allow your victim time to cry out for the guards. Sigil stone enchanted weapons deliver their enchanted damage instantly. Top level Sigil stones are available at level 17.

As amazing as homemade poisons can be, the only real instant damage poisons unfortunately, are some of the ones you can find (not make yourself). A stong poison of illness for example will instantly damage 30 health. More info on in-game poisons here: http://www.uesp.net/wiki/Oblivion:Potions#Poisons

Just turn down the difficulty slider to simulate progress. For every level I grow after level 15 in Oblivion, I decrease the slider by one notch.

Download Deadly Reflex mod, as someone else said.

You can also slit peoples throats with that mod....and decapitate people...and cut them in half.

While using mods can help to adress this issue, if you don't want to or can't use mods, I might try lowering the difficulty slider. Normally I try to avoid doing this as I'd rather win by overcoming challenges rather than making them easier, but sometimes, there's really no shame in using the difficulty slider to make your game easier, I'd say this is one of those times. After all, you're not failing to one-hit-kill enemies because your character isn't strong enough, but because of level scaling.

Other than that, I'd try making sure you have the strongest one handed melee weapon you can get, to maximize the amount of damage your attacks cause, seeing as two handed weapons don't get a bonus and the bonus for melee weapons seems to be double that of ranged weapons.

get as much fatigue as you possibly can so that if you sneak attack with a power move you do more damage. I think with +500 fatigue my orc was able to hit pretty darn hard.

This is the melee damage formula modified for fatigue from UESP wiki:

If you solve this formula for a character that has 100 or 500 fatigue, you will see the results are the same as long as his fatigue is fully topped off. 100/100=1; 500/500=1. The impact of fatigue within this formula is that it can reduce damage if it is at less than 100%. The one hit instakiller doesn't care so much what his fatigue is as he does about making sure it is fully topped off before he strikes.



When modifying melee damage for sneak and power attacks, it is important to remember this point from UESP wiki:

I could swear that my power attacks did more damage than sneak attacks then.... oh well.

yep, youve been told.DEADLY REFLEX.i use v 5.0 as the v6.0 is a pain in the ass to install.killed my game and i will not start a new one yet.but yeah DR5 is the way to go for one hit instakills.
poisons are fun and if you have OOO or the FCOM set up cuz im not sure which overhaul added them,there are poions like cyanide,burning blood(which i love using,poison an arrow,hit a fool from a distance and watch him burn),etc.also DR5 has a combustable convulsion spell that can only be used once a day but when you hit your tatrget they literally explode into peices.fun fun