Alongside cards including Laboratory Maniac, Thassa's Oracle, and Angel's Grace, Ad Nauseam makes for an alternative win condition that will end a game of Commander on the spot
or, at least, the opponent has had a chance to catch up
I think people were down on this guy because the fight ability looked better than it is at first glance, but in a format where ramp is good, this card is a two-for-one that can also finish the game
Some recent commanders that might want to consider this card in the 99 include Ellivere of the Wild Court and Galadriel, Light of Valinor

Facilier 39 $0.10 Elsa 40 $0.16 Elsa 41 $2.30 Elsa 42 $0.21 Flotsam 43 $0.23 Jafar 44 $0.05 Jafar 45 $0.05 Jetsam 46 $0.10 Magic Broom 47 $0.52 Maleficent 48 $0.10 Maleficent 49 $0.22 Marshmallow 50 $0.42 Mickey Mouse 51 $0.09 Olaf 52 $0.09 Pascal 53 $0.08 Rafiki 54 $0.06 Sven 55 $0.25 The Queen 56 $0.05 The Wardrobe 57 $0.09 Tinker Bell 58 $1.06 Ursula 59 $0.06 Yzma 60 $0.22 Zeus 61 $0.13 Befuddle 62 $0.06 Freeze 63 $0.14 Friends on the Other Side 64 $0.11 Reflection 65 $0.21 Magic Mirror 66 $0.11 Ursulas Cauldron 67 $0.25 White Rabbits Pocket Watch 68 $0.09 Aladdin 69 $1.29 Beast 70 $0.21 Cheshire Cat 71 $0.16 Cruella De Vil 72 $0.05 Duke of Weselton 73 $0.21 Flynn Rider 74 $0.17 Genie 75 $0.20 Genie 76 $0.10 Genie 77 $0.22 Hans 78 $0.05 Horace 79 $0.11 Iago 80 $0.05 Jasper 81 $1.60 John Silver 82 $0.08 Jumba Jookiba 83 $0.26 Kuzco 84 $0.19 Lady Tremaine 85 $0.13 Mad Hatter 86 $0.05 Megara 87 $0.20 Mickey Mouse 88 $0.12 Mickey Mouse 89 $0.22 Mother Gothel 90 $0.06 Peter Pan 91 $0.13 Tamatoa 92 $0.10 Tinker Bell 93 $0.19 Do It Again

For the Ancestors can be fired off twice, or just pitched and cast later from the yard