When it comes to defensive Normal-types, Wigglytuff definitely isn't a popular choice in UU, as she is horribly outclassed by Clefable, Chansey, and Lickilicky. However, with useful support moves in Wish, Heal Bell, and Thunder Wave, as well as passable defenses, Wigglytuff can still be fairly effective in that role.
Wish is a fantastic move to heal weakened teammates with, and provides valuable team support. Protect can scout for troublesome moves, and alongside Wish, forms a means of reliable recovery that allows Wigglytuff to stick around for quite some time. Seismic Toss is Wigglytuff's best form of offense against most foes, and, while it doesn't do amazing damage, it is the best option Wigglytuff has in that regard (while Wigglytuff's STAB move, Hyper Voice, might seem better, it really only does more damage against frail Pokemon like Sceptile). The last slot depends on what kind of support you need for your team. Heal Bell is a useful option if your team is vulnerable to status, while Toxic and Thunder Wave cripple walls and sweepers, respectively. However, if you lack a Pokemon with Stealth Rock, Wigglytuff can use it in the last slot instead.
Because Wigglytuff has such a massive HP stat, investing in her defensive stats first will increase her defensive ability much more than a normal spread. Wigglytuff's EVs, in general, are also slightly biased to her Special Defense stat, to allow her to better take on Pokemon from the special side, who she has an easier time dealing with than physical threats. 44 HP EVs hit a Leftovers number, which further helps Wigglytuff's cause, while the rest are poured into her physical Defense to cushion against lighter physical blows.
Bulky Pokemon, such as Blastoise, Hitmontop, and Spiritomb, who lack reliable recovery, work well alongside this Wigglytuff set, as the Wish support she provides can allow these Pokemon to continue doing their duties for a prolonged time. Additionally, Wish can allow certain sweepers such as Mismagius and Hitmonlee to come back in and wreak even more havoc. Depending on the support move in the last slot, the Pokemon that Wigglytuff can assist will vary. For example, if Heal Bell is used, Pokemon who detest certain status effects, such as Milotic, Moltres, and Hitmonlee are great partners. If Thunder Wave is used, Pokemon who can take advantage of the opponent's slower team such as Rhyperior, Aggron, and Hariyama work well. Finally, if Toxic is used, Pokemon who appreciate crippled walls work well alongside Wigglytuff.