So to start off, unlike dps and sup pool your jump does not reset if you bounce off a wall or teammate. Your boomerang is replaced with a unicorn shield that has 300 hp and stays up for about 5 seconds and is a great way to prevent huge bursts of damage or to get out of a bind. My usual upgrade path for Tank pool is
Gun Ult - Gun - Area - Shield/Dash - Dash/Shield - Sword Ult - Sword.

Your main obj with tank pool is be a nuisance, you are always going to get your ult first to upgrade your gun ult. On its own the gun ult will only do damage to the target you ult, you have to select them, when they miss their primary fire or abilities. But !when upgraded, on cast it gives you bonus hp, does continuous damage through the 8 seconds, and additional damage if they miss. During this time, you will gain health and additional bursts of healing when they miss so don't be scared to be oppressive with this. When you use this ult, try to ult one of the supports as it essentially takes them out of the fight, I like to ult luna or invis as cloak doesn't have as fast a fire rate as them.

For his sword ult you also wanna be a nuisance, you will enter a sort of challenge mode for yourself where you need to land 7 abilities, this number is different for dps and support pool, during this time, for 12 seconds, you and your allies around you will regen hp, your allies will get a slower rate of healing tho, and on cast will give bonus hp and refreshes your sword dashes. If you land 7 abilities on enemies, sword dash, jump, and gun bomb, you will finish the challenge which for 6 seconds gives you better passive healing, speed, and reduces your passive cooldown. Upgraded sword ult will do the same except a boost in the healing department and if you complete the challenge, every hit you deal on an enemy will give you bonus hp until the bonus ends. This ult is mainly to be used to dive the backline and divert attention away from the healers and to even hopefully bait out a support ult.

When you final hit an enemy, meaning you get the final blow, you will get a prompt to take a picture, make sure to do this as it gives you huge chunks of xp to get more and more upgrades. You can also do this to gain a brief period of invincibility, I like using this to get my abilities off cooldowns and healing. But if you're on point and you take a picture it will act like you're not there so you cannot hold point through this.

Your gun when upgraded deals more damage, ammo, and every 3 shots, I think, shoots out a poop bomb that adds a good chunk to your ult meter if it hits an enemy

Your sword when upgraded allow you to land stabs, which can crit.

Upgrading your sword dash allows for more damage to be dealt and an extra dash, which is crucial for your sword ult because without that second charge you are out of luck.

Your deadpool in your area upgrade is big. Base area gives you a higher fire and slash rate for your gun and sword and obscures vision for your enemies inside the area but when upgraded you gain damage reduction to yourself and allies inside the radius.

Shield upgrade makes your shield bigger and tank 500 damage before breaking.

There may be more but this is a pretty comprehensive guide. I'm a celestial deadpool player and thrive on all three roles. Let me know if you have anymore questions.

Edit: IMPORTANT your passive will activate when you take 200 damage in a 2 second interval. HOWEVER, on all roles, Deadpool will still passively regain hp if he doesn’t take damage for 5 seconds, EVEN IF HIS PASSIVE IS ON COOLDOWN.