Level 100 Statistics (see level 5, 50, 100)
You may be wondering why Tangela would even be considered for use on any team when Tangrowth exists, especially since it's allowed in UU; however, Tangela's higher Speed and lower defenses make it an exceptional user of Sleep Powder and Endeavor. However, outside of that niche, Tangrowth will always be the better choice. Just don't be fooled by the innocent look of this ball of vines; if unprepared for, Tangela can leave many opponents in despair.
Tangela is one of three Pokemon who have access to Endeavor, a sleep inducing move, and a way of patching up its poor Speed, the others being Smeargle and Tangrowth. Tangela's lower defenses and higher Speed make it a better Endeavor lead than Tangrowth, and Smeargle is not allowed in UU. The idea behind this set is to incapacitate the opposing lead with Sleep Powder, and then use Endeavor to weaken the switch-in. This is done by allowing the opposing lead to critically damage Tangela while it survives with its Focus Sash, then Sleep Powder is used to put them to sleep. As most opponents will switch out their lead, Tangela can use this turn to set up Sunny Day and double its Speed, and then follow up with a fast Endeavor to bring the switch-in to very low health. When faced with leads such as Omastar and Cloyster, it is usually better to just OHKO them with Leaf Storm before they can do anything.
Leaf Storm is the recommended Grass-type move, and is used to deal massive amounts of damage to Ghost-types who are immune to Endeavor, although Energy Ball can be used for reliable, consistent damage. SolarBeam is also an option, although the ability to OHKO Omastar and Cloyster without having to set up the sun is usually more appealing.
Team Options & Additional Comments >>>
Tangela can take advantage of its decent base 100 Special Attack and Chlorophyll to run a special sweeper set in the sun. SolarBeam, Hidden Power Fire, AncientPower, and Sleep Powder make Tangela quite difficult to switch into when the weather is sunny. However, Tangrowth and other Pokemon with Chlorophyll, such as Exeggutor and Victreebel, are usually better for this role. This is also the case for Choice Specs, which is outclassed by Tangrowth, and Choice Scarf, which is better done by Venusaur. Tangela also has access to Swords Dance, but its Attack stat is way too low to pull it off efficiently.
Checks and Counters
Tangela is difficult to counter if you do not have the right lead match-up. Ambipom and Flame Orb Hariyama defeat Tangela relatively easily, as do Choice Scarf Venusaur and TrickScarf Mesprit and Uxie. If you don't have any of these leads, however, then Ghost-types such as Mismagius and Spiritomb make good switch-ins to Tangela, as they are immune to Endeavor, although they need to avoid Leaf Storm. RestTalk Weezing and Altaria do not mind being put to sleep by Sleep Powder. Weezing can use Will-O-Wisp to break Tangela's Focus Sash, while Altaria can just set up Dragon Dance in its face.