Overview
As an Alucard player with experience of over 10k+ matches with him here's few guide from me: Alucard is a Fighter/Assasin Role hero which means his Main source is Damage. He can be played as Aggressive as soon as he reach lv. 4 which I don't really recommend that is until you don't you other choice but that doesn't mean you can't play aggressive if it's a five men or trio lobby with communication you can but to play Alucard the most effective way is to farm gap enemy since Alucard is a great Snowball hero with high burst damage. He was often known for lifesteal king or spell vamp king back day's but after the adjustments he's known for more a high burst hero. Another tip is position yourself properly Alucard main weakness is continues CC (Crowd control) his skills are mainly focused on chase burst so if you position yourself in a bad situation it will be a bad outcome for you. He is also really good counters for meta heroes like YSS, Lancelot etc. The best way to use him is to outfarm your opponent, position yourself well and know what to do when. Alucard is one of those heroes who can solo carry a whole team if played well I have a lot more to say but I'll stop here, Thank you.
Strengths
Alucard is best when he outfarm your opponent, position yourself well, know what to do when.
Weaknesses
Alucard main weakness is High continues CC (Crowd Control)
Cross
Once again emblem and build completely depends on draft pick
Cross
Emblems and builds depends on draft picks
Battle Spell
Retribution is an spell for junglers, there are 3 types of retribution from which I'll only talk about one which is often used for Alucard and is also best for Alucard. Flame Retribution. It deals 520 true damage to the creeps or minions which increases with our hero level and the passive of Flame retribution is what makes it best option for Alucard. It grants him extra early game damage which boost him significantly.
Cross
You can use Vengeance in exp to become more durable and with full build you can do 1v5 and still win. You can also best out most of the heroes.
Best With Tigreal
If your playing duo, trio, 5men with Tigreal or heroes similar to Tigreal is the best combo for Alucard.
Watch Out For Valir
There are lots of heroes like Minsi, Badang, Franco etc but with proper play Alucard and beat all of them.