1) Too powerful for it's price. Recipe gives +6 DMG, +11% IAS and +8% LS. AND uber passive. Seriously, recipe cost is too small.
2) What sunnymarcell said, T-Down on stat stealing or gain per kill. Pudge would rule the world with this.
3) I like charges from allied deaths. Honestly, i'd remove stat gain and left only this. Nice idea, and quite balanced. If you survive 5v5 clash, and all died except you, you get +60 damage until your death, which is ok.
Suggestion: remove stat gain, increase recipe cost to 4000 or even 4500. It would fit insane lifesteal
Nice concept. But think about numbers!
For mere 2100 gold you get chargeable Dagon, which deals max of 500 damage to enemy, removing also 250 mana. Or you can heal ally's mana and hp by 500. No manacost for use, no cooldown. Overpowered like hell.
Magic damage increase with prereq. of 6 charges is OK.
Suggestion: let each charge replenish 20 hp/mana to allies and remove 15 hp/mana from enemy. And even then recipe cost might be raised to 1000 gold.
Mark Of Immortal
If only target hero becomes "immortal", then it's OK. Must have really
visible effect for enemy to know, which hero is "caster", and which is "immortal".
Suggestion: mention visible effect, add some manacost (70-100)
T-Up on 2nd and 3rd items, if you make them better. But i somewhat doubt overall usefullnes of Claws, so T-Null for now.